Hello, and welcome back to the blog!  Here at NCPTT, we have been slowly returning to the labs and getting our research projects moving again.

One of the cut samples that will be used as a control during the experiment

One of these is a Technical Services research project for Florissant Fossil Beds National Monument (FLFO), examining how different adhesives used in paper shale fossil consolidation behave as they age.  The paper shale fossils from FLFO are as fascinating as they are fragile.  As their name suggests, the fossils are found in and between very thin (sometimes paper thin!) layers of shale.  This material is highly sensitive to fluctuations in humidity and temperature, which can cause the shale layers to delaminate and flake off.  Unfortunately, the loss of just one layer can sometimes mean the loss of a fossil.  One of the methods for treating delaminating paper shale fossils is to use a very thin adhesive to stabilize the layer or re-adhere a loose fragment back into place.

Treating samples with a medical grade butyl-octyl cyanoacrylate blend. The bottles for some of the adhesives are very small and only contain about 5 mL of liquid.

Our goal is to test five different adhesives to see which one does the best job at stabilizing paper shale fossils in museum collections with the least change in appearance or damage over time.  Specifically, FLFO wants to see how cyanoacrylate (super glue) adhesives age in comparison to butvar (thermoplastic polyvinyl butyral) resins.  For this experiment, I worked with experts at FLFO to choose two common short-chain (ethyl) cyanoacrylates—PaleoBond and Aron Alpha—as well as a medical grade longer-chain (butyl/octyl blend) cyanoacrylate manufactured by GluStitch.  For the butvars, we chose B-76 and B-98 dissolved in ethanol.

Prepared and treated samples, five replicates for each adhesive, organized by column. Adhesives used on each column (from left to right) Aron Alpha, PaleoBond, GluStitch, B-76, B98, and control

I’m currently in phase 1 of the project, which is looking at how these five adhesives applied to paper shale fossil samples behave under extreme accelerated weathering conditions.  This will help us understand how these adhesives break down, and what evidence of failure to watch for in the following phases.

The first step was to cut the samples.  Because the paper shale is so sensitive to moisture, I cut them dry on a diamond sectioning saw.  There are 30 samples for this phase: five replicate samples for each of the five types of adhesive, and five control samples which will be put through the same conditions with no treatment.

In order to measure exactly how the adhesives affect the paper shale matrix, I took baseline data before treating the samples.  The data I am collecting at each step are: photographs, color, gloss, surface roughness, and infrared spectra for chemical composition.

Samples treated with PaleoBond while they’re still very wet. The difference in gloss between the treated samples and the untreated samples (to the left) is very noticeable here. The gloss diminished as the adhesive dried.

With the baseline data collected, I was able to start treating the samples.  For this phase, I am not attempting to make the fine stabilizations that are commonly needed for paper shale fossils, rather, I want to see how the adhesive itself ages.  I coated the whole surface of each sample with its respective adhesive and adhered a small chip of shale to one corner.  Another round of data collection so that I have measurements of treated samples, and the samples are ready to go into the QUV weatherometer for exposure to high levels of UV radiation to simulate extreme accelerated weathering.

We don’t know exactly how these adhesives will fail.  And by “fail” we are looking at: 1) Will the adhesive alter the appearance of the sample?  Will it turn yellow with age and exposure to UV?  Will it darken or obscure the fossil? 2) Will the adhesive joint remain solid?  Will the chip fall off as the sample is aged? And 3) Will the adhesive change chemically?

We will see what they look like after being exposed to a harsh UV environment for a few weeks.

National Center for Preservation Technology and Training
645 University Parkway
Natchitoches, LA 71457

Email: ncptt[at]nps.gov
Phone: (318) 356-7444
Fax: (318) 356-9119