>> From the Library of Congress in Washington, D.C.
>> Fenella France: Good afternoon, everyone.
I just want to welcome you to today's Topics
in Preservation series.
I'm the chief-- name would be helpful.
Fenella France, chief of the Preservation,
Research, and Testing Division.
And we're delighted today-- have today here, Dr. Andrew Davis,
who is one of our chemists here in the Preservation, Research,
and Testing Division, talking about Centuries of Cellulose:
Lessons Learned from the Molecular Analysis of Cellulose
in Aged Paper Collections.
And Andrew has become a very critical part
of our preservation team, and we're really delighted.
So Andrew has a background, his Ph.D. was in polymer science
and engineering from the University
of Massachusetts, Amherst in 2014.
From there, he worked at 3M developing adhesive chemistry
and photographic processes and came to the library in 2016.
And without further ado, I will pass over to Andrew.
[ Applause ]
>> Andrew Davis: Great.
Thanks, Fenella.
So I will be talking today a little bit about cellulose
and paper materials as they age.
And so what I mean by aging-- I'll jump right into it--
is, as far as we're concerned here,
that means paper durability and paper permanence.
How does paper behave and stay preserved
over a long period of time?
And when we're looking at it as preservationists
and conservators, a lot of times we can judge it based on what I
like to call the "eyeball test."
Most of the time, you can look at an object, you can look
at some paper, and say what is bad, what is good.
Is this in bad shape?
Do we need to do something with this object, with this material?
But that doesn't always pass muster.
Sometimes you need quantitative measurements.
And there are a number of ways over the years
that people have taken quantitative assessments
of paper-based materials.
These range from chemical assessments, like pH
or inductively coupled plasma, or XRF, which are familiar
to various folks in this room
for analyzing elemental compositions
or metallic components that are in paper materials.
There's spot testing.
Again, identifying specific elemental
or chemical components in paper.
When the eyeball test doesn't work
or you need something a little more specific,
you can do optical testing
and then you can also do physical testing,
things like fold or tensile measurements
that give you a quantitative assessment of material.
But what none of these techniques address is the
underlying fundamental building block
of paper itself, and that's cellulose.
And if anyone in here remembers and really fantastic "Powers
of Ten" video where it zooms in and out
of different length scale scales.
You can see what materials or at what scales.
Cellulose really is the fundamental building block,
about as small as you can get, when you start
from the raw materials, starting from it trees
or wood-based materials or rag-based materials,
all the way down past the cellular structure,
past cell walls, past fibrils, past fibers, down to cellulose.
And what cellulose looks like is a string
of sugar molecules linked together--
that's what this N represents--
over and over and over and over again,
to make a very long chain polymer.
And there's actually even more complicated structure there,
where you have hydrogen bonding, interacting both
within a cellulose chain and between cellulose chains.
But it really is the fundamental building material building block
that makes up paper.
And when we talk about cellulose degradation,
mostly what we're talking
about is cellulose significant scission
or breakage of cellulose chains.
And the two main mechanisms that this can happen by--
and if you hold with me for just this slide,
this is about as deep into the organic chemistry as I get.
[laughter] You've got acid hydrolysis where you can break,
usually that oxygen linkage there,
and you'll take one long polymer chain of cellulose
and you'll split that up into two smaller ones.
You can also have oxidation,
where the rings often will open up.
And then these will expose some functional groups that can go
on to perform additional chemistry often
in a degradative nature, either color changes or again,
chain scissions, and start breaking down the chains.
And so when you talk about quantifying this,
how do you quantify what's happening
to the cellulose molecules that make up paper?
There's a method that's very popular in polymer science,
and that's called size exclusion chromatography.
And like any chromatography,
it separates chemical components based on some criteria.
And in this case, it separates polymeric molecules,
large scale molecules, based on their size.
And it does this by taking some samples with both large
and small chain cellulose, flows them through a porous media
that physically separates them by size,
and so the larger molecules will come out at a different time
than the smaller molecules.
You can detect them and then come
up with a quantitative measurement
of how much small chain cellulose there is relative
to large chain cellulose that you started with in your sample.
And we refer to this entire series as the distribution.
What's the distribution of cellulose sizes in your sample?
And so I'll refer to this as the distribution.
And that distribution can be captured
by a single quantitative simplification called the
molecular weight.
And I can spend an entire day talking
about how you make that's simplistic quantification.
There are different measurements
and points along this distribution you can use.
But the idea is it's one simple identifier
for what this distribution looks like.
You may be more familiar with that-- whoops--
in terms of the degree of polymerization.
And that's just another way of referring
to the molecular weight.
And so if I say "molecular weight," or if I say "degree
of polymerization," degree of polymerization just adjusts
for the size of those sugar repeat units.
But know that I mean the same thing.
And so if you're more comfortable thinking about one
or the other, you can swap those in your mind.
They are both a simplification
of that more complicated distribution.
And I'll be showing you examples of both.
I'm not going to get too deep into preparing samples
for size exclusion chromatography.
I will say that we are using a direct dissolution method.
We're taking the cellulose,
we're not doing any chemical modifications
to it from the paper.
We are directly dissolving it in a solvent system.
And so for using solvents in size exclusion chromatography,
that's been used for decades in polymer science
with synthetic polymers and plastics, like styrene or PET.
But for cellulose, it's really just been pinned
down in the last decade or so how to do this
through a direct dissolution method.
And that's because it's a tremendously complicated solvent
and solute system.
Ann Chapatist [phonetic spelling] has done some
excellent work reviewing what goes
into these different systems that you can use
to dissolve cellulose.
And so if you want to know more,
I highly recommend looking up her work.
But it does take a long time and it's fraught with complications.
But it can be done, and the method we're using is one
of the benchmark methods that is used with cellulose scientists.
It's something we use just because it's comparative
to other cellulose researchers in the field.
And so why size exclusion chromatography?
Like I said, it's a direct measurement
of the fundamental building block in your paper materials.
And it's a cornerstone of polymer science that the size
of a polymer is directly related to material degradation.
As the material degrades,
the polymer chains will start breaking.
You can measure that.
As the chains start breaking, that's intimately related
to material properties; how strong it is, how durable it is.
It also reveals minor changes that are perhaps undetectable
or only very subtly detectable by physical measurements.
And to give you an example of that, I'll use something
that we use in the lab--
that we've used size exclusion chromatography in the lab for,
a pretty big team effort that's been ongoing for a number
of years before I came here even,
on iron gall ink treatments, and this is both
in preservation research and with conservation.
A number of folks I can see
in the room who've been working on this project.
An iron gall ink is a corrosive, but historically important ink.
And you can see iron gall ink induced degradation on objects
from the library collection, as well as on lab prepared samples
from lab prepared iron gall ink.
And you can see how corrosive it is.
This is an aged paper on the right there.
And you can see that the paper tends to break
and fracture right along ink lines.
We know this.
We know this is a problem.
But to me, it seemed like size exclusion chromatography would
be interesting to see what has happening
to the cellulose molecules in the area that has been inked.
That's just a little bit of the chemistry
of how iron undergoes Fenton reactions.
Both of the bad actors I talked about before,
acid and oxidative species, are involved
with a redox reaction of iron.
So really there's a perfect storm in iron gall ink
for cellulose degradation.
And what I want to see is whether we can track any changes
of treatments that this team has been working on developing
to see what's going on at the molecular level of cellulose.
And so this is that lab prepared sample
with lab prepared iron gall ink,
and these are two control samples, starting with unaged,
so just right after inking.
And you can see this is the molecular weight distribution
from size exclusion chromatography.
And you can see that there's high molecular weight species,
up to about a million grams per mol,
is the predominant size of cellulose there.
And you have some smaller components, as well.
And you have some smaller components, as well.
And this is just in that heavily inked region,
the underlying paper.
And it gives you a degree of polymerization
of about 2800 of the cellulose.
After artificial aging, so this is high heat, high humidity,
in an oven for 28 days, you can see that all
of those high molecular weight cellulose molecules are
almost gone.
There's very little left.
They've all broken down into much smaller cellulose chains,
about 10,000 molecular weight.
Degree of polymerization reduced about ten-fold, about 150.
And so these are papers without any treatment on them.
And the question is, what are some
of the conservation treatments we could apply?
What do they do over time?
How do they help preserve, if they help preserve,
the cellulose and molecular structure.
And so I'm not going to get too deep into the details here.
This is something we're hoping to publish and get out there,
and I don't want to give away the punchline to any of this.
So I'll talk just very broadly about different treatments.
And so, for example, all the treatments I'll show are
after aging.
And I'm going to compare them to these two controls.
So all of these have been aged in an oven
after the treatments have been applied.
And you can see this first treatment
in red really doesn't seem to do much of anything.
And size exclusion chromatography can tell
you that.
You can see both the degree of polymerization is about the same
and the distribution shape itself,
the size of all the molecules in that sample, are about the same.
They look almost identical to that condition
without any treatment at all.
And if you look at two additional treatments, again,
both after aging, but these start to look much more
like pristine samples.
And so by eye, it might be hard to distinguish these two.
They both look about the same in the paper material itself
after aging, but these distributions and this degree
of polymerization measurement shows you that one
of them is actually slightly
and subtly better than the other one.
It helps preserve these high molecular weight components
in the cellulose.
You still have these million molecular weight species
that match up to if you had unaged.
So we can stick it in an oven, apply heat and humidity,
and we know that this treatment is perhaps better than this one.
And we're trying to dig a little bit into why that might be.
But that's just an example to start getting you thinking,
maybe perhaps get used to looking
at what this data might look like.
And if you noticed on that Y size exclusion chromatography
slide I showed, I talked about micro-sampling.
And a couple of the popular methods that I talked
about for quantifying paper condition take
up a lot of paper.
And so that's a scale schematic representation
of an 8 1/2 by 11 piece of paper.
And to do a physical condition test, a fold endurance test,
example, needs about half of an 8 1/2 by 11.
Similarly, a pH extraction needs
about the same amount of material.
And so it's fine on lab scale papers,
but if this is something you want to do
to a collections object, that's just not acceptable.
Size exclusion chromatography can use dozens
of micrograms of material, right?
So this is a cute little paper biopsy machine.
It's just a kind of tiny hole punch that punches out samples
that are about one millimeter in diameter.
And those can perhaps be taken from collections objects,
from blank pages in a back of a book, from detritus
that has been shorn off of a very fragile material,
and that's perhaps a little more acceptable.
And so the question is, how can we apply this
to actual collections items or perhaps books?
And so I wanted to start using this on a collection of books,
and the books that immediately came
to mind were the Barrow Collection.
And William Barrow may be a familiar name to some
of the folks in this room.
He was a paper chemist, did a lot of work in the 50s and 60s
on naturally aged paper chemistry and what's going on.
And here, William Barrow is working on a fold tester.
There's Cindy Ryan from our research group doing her best
William Barrow impression.
And if you haven't seen a fold tester, I'm a big fan of them.
They're very visceral machines.
You get a real sense of what's going
on what a fold tester is operating.
And what William Barrow was trying to do was he was trying
to connect physical properties to chemical properties
in naturally aged books.
So taking a naturally aged collection
and seeing how you can connect the chemical components in paper
to the physical condition of the durability
and brittleness of that paper.
So I'm going to take a bit of a detour now, and I'm going
to step away from all of the technical science stuff
and give you a little bit of history
about William Barrow and the Barrow Labs.
Like I said, some folks may be familiar
with him, some folks may not.
And it's kind of an interesting story.
And so Barrow often times gets a lot of credit
for being the originator of research on pH
and alum-rosin sizing and its effect
on naturally aged materials.
But it built on a lot of work
that had already been going on in the field.
Kohler and Hall in Sweden
in the 20s had done perhaps the first definitive connection
between acidity and paper deterioration.
There was then a lot of work done in the 30s
at the National Bureau of Standards,
at the Government Printing Office,
in the National Archives,
looking into the fundamental science of paper degradation,
looking at whether fiber processing is more influential
than the fiber source, whether ground wood papers have a
different effect on paper longevity than rag papers,
on whether sizing and the acidity that's inherent
in sizing effects paper degradation.
William Barrow was a book binder
and a craftsman before he started looking
into the chemistry of materials.
And he started looking into the chemistry of materials
and he started working with these researchers
in the National Bureau of Standards
in the National Archives, learning chemistry
from them at that time.
And that kind of sparked his interests from just book binding
to the more fundamental chemistry of paper conservation.
And it led to his interests spanning that type of chemistry,
ranging from cellulose acetate lamination, to deacidification,
to aging of book papers, both artificial and natural,
to the manufacturing of durable papers.
And I'm not going to talk too much about it,
but it's impossible to talk about William Barrow
without talking about cellulose acetate lamination.
And so he spent a lot of time developing, refining,
and pitching the idea of cellulose acetate lamination
as he learned alongside these researchers at NBS
and the National Archives.
And this was during the 1930s, took a lot of input
from Bourden Scribner, who was the chief of the paper section
at the National Bureau of Standards,
worked with Arthur Kimberly, chief of the Division of Repair
and Preservation at the National Archives at the time.
It involved development of visits to the National Archives,
prototyping with the Mariners' Museum in Portsmouth, Virginia.
And he came up with this method
for cellulose acetate lamination, patented,
oddly enough, with all of that collaboration with just his name
on the patent in 1941.
And that's really where Barrow got his claim to fame.
And after that, he received a grant from the Council
on Library Resources to do studies on paper and book aging
in Richmond, Virginia at his labs,
and this was in the 1950s and 60s.
And William Barrow said about this,
perhaps in a quote illustrative
of the work he was undertaking there, "The task of the ester is
to find, among the hundreds of possible tests
of the characteristics of a material,
those which are really meaningful, i.e.,
those which can be shown to correlate
with actual experience in use."
And so to undertake this research,
he collected a thousand books.
These were a thousand actual books spanning
about 400 years of print dates.
So about 400 years of natural aging in this book collection.
All sorts of different compositions, whether they came
from wood pulps, whether they came from rag fibers,
different geographies, mostly from western Europe,
a lot from the United States, but obviously
that included different climates, as well.
And his goal was to start doing tests on these books
and to correlate, like I said, physical properties
with chemical properties.
And the initial tests were
on about 500 books spanning the range from 1800 to 1900.
Those eventually ballooned out by another 500 books,
going all the way back to 1500.
And those included physical tests of, you know, strength
and durability, by fold testing, like I showed you,
and tear testing, which is exactly what it sounds like.
Chemical tests started off with acidity
and rosin testing expanded out to looking at alum content
and metal carbonate content and fiber analysis, as well.
What type of fibers were in there?
How large the fiber size was.
And these are pictures, not quite as fun
as the animated pictures.
But from the written reports from William Barrow, 1950s,
showing the equipment he was using.
And if you look through these reports from the 1950s and 60s,
actually what I find a little bit more fun is they are very
1950s in their presentation.
He is showing some of the researchers from the lab here.
It wasn't just William Barrow, for example.
Here is Mrs. Virginia Roberson, both technician and secretary,
putting samples in an aging oven.
Mrs. Patricia Turner working on the fold tester.
Mrs. Emily Parr taking pH measurements.
So these are very much of the time, but kind of fun pictures
that are shown in the Barrow reports.
Shows you how many people are working in the lab here.
And the lab from William Barrow produced pages and pages of data
about pages and pages of books.
And after he collected all these data,
he started making correlations.
So for example, year of manufacture,
checking the tear strength.
How does tear strength in naturally aged books change
over time with printing?
How does pH and acidity and chemical content change
over time with printing?
And then how do you correlate those?
That's down at the bottom there.
Some of the correlations between alum content and acidity and how
that interfaces with age of production of the books.
And so the conclusions of the Barrow Lab came out
and they were summarized.
You know, the effects of acidity, the effects of alum,
the effects of fiber type.
High acidity, low pH tends to lead
to poor physical conditions.
The presence of alum is usually a bad indicator,
unless it's present alongside calcium carbonate.
Fiber type, wood pulp type papers tend to be
in worse conditions than rag type papers.
The mid-1800s onwards showed to be particularly problematic.
It was, again, the perfect storm of all
of these components coming together.
And those ended up being in--
interpreted by Barrow's suggestions
on paper manufacture, what can be done to make more durable,
more permanent papers, as well as work
on comparing artificial aging
and rigorously controlled natural aging studies.
And really, it was never explicitly concluded by Barrow,
but the conclusion here is those results really, right,
are not new conclusions.
The work that was done by the National Bureau of Standards,
by the National Archives in the 20s and 30s new
that acidity was bad, knew that alum-rosin sizing was bad.
But what this proved was that those results held
in actual naturally aged book collections.
Not just any naturally aged book collection,
a really ambitious naturally aged book collection,
a rather ungainly naturally aged book collection.
So the fact that you could take those conclusions
from test papers at NBS or government printing office
and say, we collected a thousand books from all over,
all sorts of ages, all sorts of compositions,
and these results hold, is rather impressive.
There were lots of conclusions about Barrow's work.
He is often interpreted as the originator of results on pH
and alum-rosin and wood content.
For example, Rutherford Rogers, who was the University librarian
at Yale, 1985, was talking about Barrow and said,
"Barrow startled the library world with his results."
Right? So it's not-- it's not uncommon
to see Barrow interpreted as the originator of these results,
even those some results came before him.
And his lab is not entirely innocent in this perception.
If you look at the citation records in these reports,
starting with the very first one in 1959, about a third
of them had in their technical citations,
work from the National Bureau of Standards,
work from the National Archives.
By the last report in 1967, most of them had disappeared,
less than 1 in 20 were from those sources.
They were mostly self-citations of the Barrow Lab.
And so some other folks have become critical
of that assessment.
Nicholson Baker, who is perhaps a little bit infamous
for his critique on library sciences, the total extreme
of the criticism here,
really questioning why Barrow did any invasive testing
to begin with.
He said, "If Barrow hadn't chosen to destroy
yet another page in order to perform his parlor trick,
the recipe for chicken a la Terrapin would very likely be
with us today."
[ Laughter ]
So you can find both assessments in the scholarly literature
about William Barrow, that he really had this large
influential role to play in paper science,
and that he was just duplicating others' efforts.
And so I would say that my personal opinion
of William Barrow is a little more sympathetic with that
of Barbara Higginbotham and Sally Cruz Roggia.
And a lot of this history comes from Sally Cruz Roggia.
She did some excellent work.
I highly recommend looking up her deep dive
into William Barrow's history.
Saying that, at the time that that original research was done
in the 20s and 30s, librarian-- conservation minded librarians
at the time were more interested in durability
and in-use durability, in taking a page
and making sure it's not breaking while users are
interacting with the books.
And so the reports from the National Bureau of Standards,
from the Government Printing Office, were highly technical,
highly constrained to the government.
Didn't make their way much to librarians
that did a lot of work.
For example, here's at the Enoch Pratt Free Library,
just doing mending and working to make sure
that the books could be used and were in good condition for use.
And Barbara Higginbotham
and both Sally Cruz Roggia make the argument
that Barrow is the great promoter here.
He's the one that takes these results and perhaps
by using a collection of a thousand actual books from all
over the place, a little more representative
of what is actually in libraries.
It's something that can be, you know,
connected with on a visceral level.
And so while he may not have done exactly the original
research, his results were widely influential
for a good number of reasons.
And so after William Barrow's work, the books found their way
to the library here
in Preservation Research and Testing.
And the value of these books now is entirely
in their scientific content.
They have been destructively tested.
There are very few books, going back to the 1500s,
that have had pages ripped out of them
for tear testing and fold testing.
And the fact that we can still do this adds tremendous value
to that collection.
And so those were donated to the library in the 1970s.
They've since been rehoused, sorted, and barcoded.
Now they're in PRTD Center
for the Library Analytical Scientific Samples.
They serve as kind of a small scale museum of book art.
You can take them apart, look at what's going
on with different books over different times.
But they do provide another opportunity for research.
There's been progress in material science.
There's been progress in polymer science.
Polymer science was barely a field
when Barrow started his work.
There's been improvement in analytical
and instrumental methods since the 1950s.
For example, size exclusion chromatography.
And as a study of natural aging, it's kind of interesting
that there's been another 50 years of aging.
And we'll go back to Rutherford Rogers,
that librarian from Yale University.
We'll finish out his quote that I gave you a taste of before.
"Barrow startled the library world with his research results,
which suggested that only three percent of the papers published
between 1900 and 1949 could be expected to last
for more than 50 years."
William Wilson at the National Bureau of Standards,
around the year 2000, could do the math, and said,
"It's almost the end of the century and somehow,
most of those books haven't known
that they were supposed to disappear."
[laughter] So some of the conclusions
from that data obviously need revisiting.
And so one of the tremendous efforts
that have been undertaken in PRTD is digitizing those pages
and pages and pages of data.
So there are a thousand books.
There's about 16-ish data points each.
I say "-ish," some books are missing a couple of data points.
So that gives you 16,000 data points.
And they fall in all types of categories.
There's time and chronological data,
what year they were published.
There's categorical data, what cities they were published in.
There's binary data, right?
Yes or no, simple thumbs up, thumbs down.
Is there alum, is there not alum?
And then there's numerical data, pH and fold data,
which can span any range of numbers.
And so while William Barrow had all sorts of, you know,
interesting methods and techniques and technicians
and secretaries working for him,
what he didn't have was a desktop computer.
And so now we can look at these correlations again
and the first thing you can do, once we digitized all this,
is plot out all of the raw data, the entirety of it.
And it's not as pretty as perhaps it once looked.
There's a lot of scatter.
There's a lot of outliers.
And that's not unexpected.
These are real books with unknown histories from all
over the place, and who knows where they were
at what point in time.
But it just goes to show how messy it can be.
One thing I've done is started manipulating it a little bit
to see if there's anything else you can learn.
So let's move away from the big scatter.
These are some box plots.
I know box plots probably something you haven't thought
about since high school.
Honestly, not really something I've thought
about since high school.
But they do give you a statistical snapshot by decade,
instead of Barrow's plots,
which were just median values by decade.
You pick the median value.
And it gives you nice clean plots.
This gives you some more data on what's going
on in the distributions over time.
For example, if you've got a keen eye,
and the projector's colors are behaving themselves,
you can see that the data is right skewed.
What that means is that the average value
for a decade is higher than the median value for a decade.
You've got a couple of odd, high-end outliers usually,
for each decade, that pulled data toward the right.
Most of the lower performing book.
There are more lower performing books
than there are higher performing ones,
pretty much across the board by decade.
And you can do this for any of the any of the data.
For the fold data by year, for the tear resistance,
for the chemical properties.
And so what that does and what I like doing
when I do this analysis is it takes the original data,
what Barrow was looking at-- he had this original data,
we have this original data, we start with the same numbers.
He's going just taking the median values,
making nice cleanish plots.
And then we can take it and we still get the same trend line.
You can see up to about 1700, there's a pretty even plateau
in physical properties and then it declines precipitously.
But you don't lose the data that you lose in the representation
of data using just median values.
You can also do some nice heat mapping to start looking
at combined variables over time.
So these are now three variables in one go, looking at year
and pH and how fold endurance changes
over time with both of those.
Right? The hotter values correspond
to higher fold endurance.
You can do the same with tear resistance.
Both are physical measurements.
Right? You would expect physical measurements,
the physical durability of the books,
to kind of match each other.
And you can see in some cases that's true, right?
In the 1650s to 1700s-ish, that high pHs, so non-acidic.
That's true, they both match.
But then it's very easy to reveal these odd little outliers
that I don't have answers to yet,
about why there's a couple books in here, in about 1850,
that are acidic that have really high tear resistance
but don't have corresponding fold endurance.
And so data manipulation and representations
like this are something you couldn't do in Barrow's day.
And they're something now that we can start looking at
and figuring out what's going on.
And so I'll jump back now to the technical stuff I started
with at the beginning about cellulose and size
and what's going on with cellulose size in these samples.
The Barrow data has macro-scale measurements.
What's happening at the physical hand scale of brittleness?
It has all the way down to chemical level information,
whether there's alum present, whether the--
you know, what the acidity is, which really is just a measure
of effective ion concentration.
But it's missing this intermediary scale.
It's missing what's going on at the size scale
of the cellulose molecules.
And so we come back to micro-invasive testing.
That's why this collection was so interesting to me
to use micro-testing on, is
that this is an actual book collection, it has data on it.
It's something we might be able to correlate
to actual collections objects,
and we can use now very small minimally invasive sampling
to get another data point
on this interesting book collection.
And so the first thing that I did is--
so I've got data points now on about a hundred
of these a thousand books.
Molecular weight values of the cellulose
in about a hundred of the books.
And you can check that against the original Barrow measurements
of acidity.
And you can see that above neutral,
there's a lot of scatter.
But below neutral pH, in acidic books, there's a decent,
pretty good correlation between acidity and size
of your cellulose, the molecular weight,
the DP of your cellulose.
And the first reaction on seeing this plot is, well, duh.
[laughter] Right?
As it's more acidic, your cellulose is going to break down
and you're going to have smaller,
lower molecular weight cellulose.
That's not terribly interesting.
But it is interesting that this is a real world collection
of books.
These aren't lab scale papers.
These aren't things that we've prepared
and artificially aged in the lab.
It's a real world collection of books.
It's unknown history.
We don't know if any given book in a collection sat
in grandma's attic for a hundred years.
It's unknown geography.
It may have been printed in Italy,
but did it then spend the rest of its life
in Sweden before it found its way to the collection?
We don't know what the housing was like,
we don't know the composition.
There's sizing all over the place.
And we can draw essentially a fairly universal trend line
between acidity and molecular weight
in actual book collection objects.
That's a powerful method.
And so how do they correlate to physical properties?
These are color-coded.
It may be hard to tell by decade.
And so you can see, as the books get newer, less aged,
they actually are in worse condition.
That's not a surprise to any of us.
Books from the 18-- middle to late 1800s are
in worse condition than the older ones.
The physical condition is lower.
The molecular weights are lower.
The cellulose size is lower.
But a lot of Barrow's data used pH as one
of the primary indicators of paper condition,
arguing that if you know pH, if you can control pH,
if you can measure pH and acidity,
you can predict what the physical condition
of a book might be like.
And what we can do is we can say in this regime,
before you start seeing a lot of scatter at the high end,
that the molecular weight, the DP, actually correlates
to physical properties closer than the best predictors
that Barrow had at the time.
So there's some physical meaning here to the size
of the cellulose and what the physical condition is of a book.
And that's really seemingly a powerful tool to use, you know,
about one millimeter diameter of a sample to be able
to tell you something about the quantifiable condition
of a piece of paper without having to take that half a page
of an 8 1/2 by 11 sheet.
There's also this question of what's been going
on in the last 50 years.
So this is Riley Thomas.
She was working with me
as a junior fellow this summer looking
at both molecular weight measurements.
She was responsible for some of those data points that you saw
in the last couple plots.
But also looking at the dynamic changing over time, right?
The Barrow data is nice.
You can say what happened to a book 300 years ago,
but it is a snapshot at this moment in time.
It doesn't answer the question
of what's happening dynamically with the books.
How are any of those properties changing
over natural aging conditions?
And so what Riley measured was acidity and compared it
to Barrow's measurement for acidity of the same books.
And so what I'm showing here is just Barrow's lab's measurements
of acidity, the recently measured acidity.
If we measured the exact same values as Barrow,
they would fall on this straight line.
And we see that at low end, that's kind of true.
At the high end, that's kind of true.
But in the middle, they tend
to start deviating consistently lower than you would expect.
And we, again, don't have a good answer why.
I have a couple of ideas.
Maybe there's enough buffer alkaline reserve
in the non-acidic books that it prevents any significant pH
changes over time.
Maybe these acidic ones have kind of bottomed
out at the most acidic values that they'll get to.
And it's the neutral ones that you expect to change over time.
Just a thought.
We don't have any proof of that yet.
Also looked at physical testing data.
Same scheme here.
This is a lot more concerning.
The physical condition, here measuring by fold data.
If we would expect everything to fall in the same line,
that's not what we get.
In fact, everything is a lot lower.
The condition of the books physically is changing a lot
more rapidly for the worse than the chemical properties are.
That's just a zoom-in of that really clustered region
down at the bottom.
And so there's this question
of the physical properties changing,
seemingly to change very fast.
The chemical properties, in terms of acidity,
perhaps are changing a little bit more slowly.
And so what's going on?
And this is something that size exclusion chromatography might
be able to shed some insight to.
This is what I've started doing some work on now.
This is stepping aside from Barrow for a second,
talking about artificial aging of book paper.
You can see that even after just one day,
that's that green arrow there, there's a drop
in physical properties.
And that's something we can measure
by size exclusion chromatography.
You can see changes in the distribution of cellulose size,
even after just one day of aging.
These higher molecular weight components are starting
to go away.
They're starting to be replaced
by smaller molecular weight components you expect
from chain scissions.
Overall molecule weight averages start going down.
And you can see that, even just one day of artificial aging.
And so if you look at these, what's a little bit deceptive
in these plots is it doesn't tell you anything
about the individual books.
You lose sight a little bit
of which book is connected to which data point.
And so I've pulled out two here, pointing to them, red and blue.
So the blue one is from 1664.
The red one is from 1745.
These were their pH values, the old one, the new one, for both.
And so these were books, one that was non-acidic in nature,
one that was about neutral.
You can see there's a dramatic reduction
in the fold endurance of the neutral book.
There's an even more dramatic change, not in terms
of raw number, but in terms of overall fold strength.
You're losing almost-- you know, almost, you know,
down to ten percent of your original fold strength.
This one, not quite as much.
And can you tell anything
in the molecule weight distributions of those books?
And what's perhaps interesting here is this book,
the one in red, the one from 1745 that showed
that big overall reduction in fold endurance starts
to show a tiny shoulder showing
up in the lower molecule weight region.
What you would expect to see from the result
of the beginnings of chain scission, perhaps showing
that there are really detrimental effects
on physical properties with even just this really small amount
of smaller molecular weight cellulose starting to form,
that you may not be able to see from pH measurements alone.
Right? This pH change, whether you go from 7 to about 7 1/2,
whether your measure is effectively unchanged
and shows you that this book is not acidic at all.
Doesn't quite match up with the physical properties
you're seeing.
Whereas these changes in the size
of the cellulose is something that does start correlative.
Now, that's something that I've found in general to be true,
that the books with low fold endurance,
with low physical properties, start having these really subtle
but indicative shoulders appear
in the lower molecular weight regions of the cellulose.
Now, you can see something is happening
that perhaps is not revealed
in other measurement techniques that have been used.
And so technical conclusions.
I hope I've showed you that micro-sampling
by size exclusion chromatography,
just one millimeter of sample,
something that I've been developing and starting
to use now on the Barrow collection
to show how it might be used in real books, can be useful either
in addition to other measurement techniques or as a replacement
for other highly invasive techniques.
It reveals some new insights into the chemical mechanisms
of degradation that you may have been misled
by measuring other physical measurements alone.
Having that Barrow data is also nice.
It gives us additional statistical analysis
and correlations that haven't been done before.
They're things that we can build on.
There are things that we can keep investigating,
looking at that dynamic age based tracking, right?
And so thinking about dynamic age based tracking
and what's changed over the course of 50 years.
I want to talk-- I want to take the last minute
to talk a little bit of my thoughts just in general
on the Barrow Labs, and hopefully you'll indulge me
in getting a little bit philosophical for a moment
to discuss what I've taken away from working
with the Barrow Labs collections.
I've been really glad to be able to work with such an esoteric
and unique collection.
And the thing I'm most impressed by when I look at Barrow's work,
when I add to Barrow's work, is not necessarily their insight
or even their outreach
in promoting what the chemistry is of book paper.
The thing I'm most impressed by, by the Barrow Labs
and the collections that we have is their notes
and their diligence.
Right? Leave it to a lab that's conserved--
that's concerned with paper permanence
to find a permanent home for these objects and these data
in a naturally aged collection spanning half a millennium.
It shows, to me, and really highlights to me
and has stressed the importance to me, the importance
of technical notebooks and technical note keeping
and keeping track of everything that you've done, particularly
for people who are concerned with preservation
over the natural lifetimes of materials, right?
I hope that my notes are as useful someday
as Barrow's notes, even if it's in regret, right?
[laughter] If, God forbid,
I do something that's regretted later on,
hopefully no one should go back and look on any of my work
and say, what the hell was he thinking?
[laughter] And should know what I did
so that they can go back and change it.
And so it strikes me as especially true
when discussing natural aging, right?
It's the nature of the job as preservation researchers.
Odds are good that none of us will see the results
of our labor, for good or for bad.
Right? It's the nature of long-term preservation.
It's the nature of working with materials where our goal is
to have them outlive us.
Right? We could mess it up badly.
But I hope everyone else is inspired here to let no one
to be able to say, what the hell where they thinking?
[ Laughter ]
So I'd like to thank a lot of interns who have worked
on this collection, a lot of staff in PRTD who've worked
on this collection over the years, making it look nice
and pretty and archivally housed and digitized,
which was a tremendous effort.
As Fenella mentioned in the very brief bio,
I do not have a conservation
or preservation background before I came here,
so I'm especially thankful-- I'm thankful to all the PRTD staff.
I'm especially thankful to Cindy and Lynn and Amanda,
who have helped kind of guide me into the conservation
and preservation world a little bit.
There are a couple references
that have helped me along the way
that I've referenced pretty heavily.
Sally Roggia, for example.
But I'd be happy to take any questions
or comments if you have them.
Thanks.
[ Applause ]
>> Fenella France: So we'll open for questions
and for the benefit of our-- external viewers,
I'm going to ask Andrew to rephrase the question
so that they can hear it.
[ Inaudible ]
>> Hi. This might be a bit too complex to get into,
but I'm just curious how you isolate or purify cellulose
from paper, which has obviously tons of other stuff in it.
And then how you, from that, are able to make sure you--
you know, you don't select
for non-degraded [inaudible] incorporating artifacts.
>> Andrew Davis: Yep, and that's a concern.
And I didn't dive too deep into it.
So-- sorry.
The question for online is how we make sure
that we isolate the cellulose from the paper and make sure
that we're not introducing other artifacts
by selectively removing parts of it or not removing parts of it.
And I would say that a lot
of the work has been done before me.
That's the hard work that had been gone
on in fundamental labs.
And that's what I was talking
about in this sample preparation that's fairly non-trivial.
It involves a lot of solvent exchange steps,
including warm water, including ethanol,
including dimethylacetamide, and that removes some of the inks.
It removes the sizing, if there's gelatin sizing,
if there's any kind of large-- also large polymers,
protein-type materials that are in there.
There's all of these insoluble components, too, right?
Fillers and lignin.
Lignin, especially in wood pulp paper,
very large scale, big molecules.
Those get separated out by centrification and filtration.
We use very fine mesh filters.
And the crux of it is this solvent system,
this lithium chloride dimethylacetamide
solvent system.
And there's been some really fundamental work on the physics
of that using light scattering to show
that it is a good solvent, by which I mean cellulose,
up to 10 million molecular weight dissolves well
in this solvent system.
And so if we know that cellulose is well-dissolved,
if we know that we're removing all these other fillers,
that's about the best that we can do.
I can't say for sure that if there's degraded, you know,
lignin, little bits of lignin that have broken off
that skew the averages one way or another.
If there's little bits of gelatin sizing
that have degraded to smaller molecular weight
that can survive and get processed into solution,
that those aren't skewing the results one way or another.
But it's about the best that anyone has come up with so far.
>> Thanks.
>> Andrew Davis: Does that answer your question?
>> Yes.
>> Andrew Davis: Okay.
>> You mentioned something about a punchline.
Can you at least give us clues as to
which journal you might publish in
or what you might call your article and/ or when?
[laughter] Because that was quite a teaser.
>> Fenella France: So that can be linked to the website and go
out as an ROC [inaudible] next published.
So we can get that to you.
But there's also some great work that he mentioned that--
you know, in collaboration with conservation.
So yeah, we'll make sure [inaudible].
>> This is Judy Biggs, I'm the team lead on the project
that you're referring to and the work [inaudible] working
on the publication at the moment and deciding where it'll be.
So we'll keep you posted.
Andrew's work is the last part of this that we're--
that was really kind of fundamental to the project,
so we're just looking forward to [inaudible].
>> Andrew Davis: Sorry.
For listeners online, we're just discussing publication
and how results are going to get disseminated over time.
But we'll be keeping people abreast
who are interested in it.
>> Fenella France: Charles?
>> If you want to use a molecular size
or molecular weight as a measure of the quality of paper
and you're wanting to evaluate degradation,
time of historical samples, how much variability would there be
in molecular weight or size of the original material used
to make paper, depending on source, species, et cetera?
For instance, cotton versus wood fiber?
>> Andrew Davis: Mm-hmm.
So the question was checking--
if you're measuring the molecular weights
of naturally aged historic samples, is there anything
that can be said for the original molecular weights,
particularly as it concerns, say, the sourcing
of the material or the process, making the material,
wood pulp versus cotton.
I get you, right?
>> Yeah, how much variability is there in the starting material?
>> Andrew Davis: That's something that I've been working
on in the lab here using our paper reference materials
in CLASS, Center for the Library's Analytical
Scientific Samples.
We have various wood pulp papers.
We have various standardized papers.
We have rag papers.
We can go back to these papers
and look whether they're rag papers,
whether they're wood pulp.
And so the question about what's the variability
in them is something I can't quite answer yet.
I don't know.
And we can't go back, obviously,
and measure where these books started from.
So we don't know how they've been changing over time.
But in terms of the papers themselves, we can start
with our lab papers that have been, you know,
historically prepared or that are rag papers
or that are wood pulp papers
and subject them to artificial aging.
>> So [inaudible] materials.
>> Andrew Davis: Right, right.
But we could start with--
we'd obviously measure the molecular weight at the start.
And I don't have an answer yet.
There's no easy trend to be drawn between--
>> When you go back and look at cotton, do you see a difference
between Egyptian cotton and some other species?
>> Andrew Davis: That I have not done yet.
And that's a good question.
>> Fenella France: We had one question from online.
Is there any one thing
that Barrow could have done differently
that would have been more informative in hindsight?
[inaudible]
>> Andrew Davis: Oh, boy.
[ Laughter ]
>> Fenella France: Can you try and remember anything--
[laughter] Can you repeat [inaudible] Andrew?
>> Andrew Davis: So yeah.
So the question from online was, was there anything
that Barrow's labs could have done differently in hindsight
that would have been more helpful?
I'd say they did a pretty tremendous job.
That's much more data than you expect to get
from most researchers.
That's dodging the question a little bit, I know.
[laughter] I would say that [pause] you know, some of the--
where different samples were taken in different parts
of a book would perhaps have been a little bit interesting.
We can go back and flip through his books and see
where pages have been torn out,
but we don't know whether those pages were used
for tear resistance in the cross-print direction
or tear resistance in the machine direction
or any of these things.
And so again, a plug for PRTD, where we've got class D coming
up with meta-data, where we're tracking which pages are removed
for which tests and what data is connected to what.
I think that's-- that would have been interesting
to have kept track of because we do see some differences whether
you take a sample from, you know, the bottom edge of a book
versus the middle of a book.
Or the middle of a page versus the edge of a page.
There are some slight differences.
If you take it from the front of a book or the back of the book
or the middle of the book,
there's a little bit of differences.
And how much those differences come out in his data,
that would have been interesting to know.
>> Fenella France: We have one more question here.
How were the physical-- how were the physical locations
of the samples within each book selected?
[inaudible] material edge or [inaudible].
And were you able to choose similar locations [inaudible].
>> Andrew Davis: Yes.
So-- one thing we've been-- one thing Riley Thomas,
who was working here, was also interested in is
where are we testing, right?
And so I'll use one of her slides.
And this book was only--
not quite accidentally chosen for this past week.
[laughter] Kind of timely appropriate, it's the 1800s.
Study of the Sky, with a chapter on the moon and eclipses.
But Riley was interested in where you're sampling.
And so the first answer to that question is,
I can say that we've been consistent
with these molecule weight measurements
against Barrow's data of picking just away from the margins
and away from the text block, towards the bottom of the page.
And every sample we've measured so far using this method has--
from in a book has gone from that spot, just for consistency,
from a randomly selected page in the middle,
not close, to either end.
We do see differences, depending on where you check.
And that's something that needs a little bit of work to figure
out and a little bit of work to systemize over time.
And that I, again, don't have a terribly good explanation for.
But for now, consistency
within the Barrow book collections is what we're
going for.
>> Fenella France: Any more questions in house?
Well, thank you all for coming.
As you can see, this is still a work in progress.
And maybe in a year or two years,
we will do the next installment and also the wonderful research
from conservation, when that comes up.
So please if you could join me in thanking Andrew again.
[ Applause ]
>> This has been a presentation of the Library of Congress.
Visit us at loc.gov.
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