Author: Catherine Stephens

NB: Before I try to blog about this talk, I need to say that…well, we didn’t really ever get to discussing Photoshop Assisted spectroscopy! Meaning, this blog will contain some interesting tidbits but you won’t be learning much about this technique or how you might use it in your lab/institution. Sorry!

The project highlighted in this talk was the analysis of the logbooks and writings of Dr. Nirenberg, a Nobel Laureate. Dr. Nirenberg cracked the genetic code (our DNA) and his writings are considered a national treasure. The bad news is that all of his writings were made using ballpoint ink and ballpoint inks are notoriously fugitive. This project used the Photoshop Assisted spectroscopy (is this just kind of like hyperspectral imaging???), and interviews with Dr. Nirenberg’s former technicians to figure out what different markings mean in the logbooks and writings (eg, there are occasionally red marks in the books which were used by Dr. Nirenberg to indicate points/data/results of interest). Also, drops/stains on the charts/files turned out to be because solvent was accidentally dropped onto the books during lab experiments.

http://en.wikipedia.org/wiki/Marshall_Warren_Nirenberg

INKS
* First ballpoint pen was patented in 1818; the pens were used to mark leather
* The inks contained within are not very archival and weren’t designed to be
* Ball ink is used by some artists and it will fade with time
* There are a lot of components in ink; dyes and pigments; solvents, resins, emulsifying agents, lubricants, viscosity modifiers; optical additives; anti-corrosives;
* The rolling ball at the tip of a ballpoint pen is supposed to plow through the ink, pushing it onto/into the paper. You can get buildup of ink at the front of the pen if the pen doesn’t work well and results in those goopy clumps you sometimes get;
*As soon as the ink comes out from the interior, the ink is oxidizing
*The roller ball can pick up residue from the surface of the paper and roll it back into the ink reservoir – this is not good because you can get a build up of garbage interacting with the ink.
*All new inks that are out there have fluorescing agents in them – to make ink look brighter with the artificial lighting used in most office spaces – this is a way you can differentiate modern inks from older ones when examining documents
* ballpoint ink pens is a $20 Billion/year business; the entire idea is for you to keep buying these products
* Before 1949 – inks in pens were oil based; these inks are very stable and you can use this information to help you differentiate when inks were applied to a substrate
* black ink is black because it has all the chromophores in it; when it degrades/separates, it changes color; other colors fade
* All inks have different fingerprints

When you get a historic document, you don’t know starting point of original ink. But you can look at the current state of the ink and you can start to understand degradation process.

SCANNING DOCUMENTS
A scanner is actually a spectrometer. Every pixel has an RGB value, but the computer mixes the colors for your eye. However, you can use those same values in a more creative way: If you consider the RGB values as values for a three dimensional space, you can use the values to plot them on a 3D map and track different types of inks used on historic documents.

*nb: the title of this talk, the author list, and author order all changed from what was published in the program. If I have left out an author name, I apologize.

The focus of this talk was to discuss the application of atomic layer deposited films of aluminum oxide (Al2O3) onto sterling silver surfaces. Ultimately, it is hoped that this process will be refined for use with sterling silver art objects in museums.

The overarching goals of this project are to find a coating for silver that is long lived; slows the diffusion of sulfur to the surface of the art object (I learned this fact at the presentation by Zeev Rosenzweig at the RATS luncheon); can be rapidly applied and covers the object homogeneously; is removable; and is less labor intensive than manual application and mechanical polishing.

(wow, that’s a lot!)

The University of Maryland has a “BENEQ TFS 500”, a commercially available atomic layer deposition (ALD) machine/instrument, to deposit thin film coatings on anything that is placed inside of it.
http://www.beneq.com/tfs-500.html

Awesome facts of this instrument:
• Samples placed in the instrument can touch one another and it won’t affect deposition;
• You can coat MANY samples all at the same time
• You can control the thickness of the layer you deposit onto the objects you place inside the instrument, down to the nanometer (nm) thicknesses
• Coatings are incredibly uniform
• The films made are dense (ie, tightly compacted), and these types of films make good vapor barriers
• Coating will go into very small crevices and tool marks
• Tailoring thickness allows you to control optical properties
• It can take a mere 1 hour to make a coating that is 100 nm thick

The project is currently examining whether aluminum oxide coatings perform better than nitrocellulose ones. They used accelerated aging studies (40°C, 30-50% RH, 20 ppm hydrogen sulfide pumped through a sealed chamber) on coated samples and performed Tarnish Rate Analysis (never heard of this!! measure color of tarnish; correlate to thickness of tarnish layer), X-ray photon spectroscopy (XPS), secondary ion mass time of flight mass spectrometry (SIMS-TOF), and atomic force microscopy (AFM) to analyze this.

RESULTS and CONCLUSIONS:
* A 80 nm aluminum oxide coating outperformed a microns thick nitrocellulose coating because it is more tarnish resistant than nitrocellulose.

* They said that that these results are very fresh and new but that the aluminum oxide coatings are removable with a minimal loss of surface copper and silver using dilute sodium hydroxide (NaOH) but that you have to be careful about the concentration of the NaOH because it can selectively remove copper over silver from the sterling silver alloy itself. But that we should all relax because the amount of copper or silver being removed is on the nanoscale.

Q&A session:

Comment: Eric presented removability study with weak NaOH compared to data from Glenn (I don’t know if this work is published or has been presented elsewhere), who used three different chalks (all of which were in the lab);

Q: is this atomic layer deposition instrument expensive?

A reactor costs…$500K. BUT you can build one or buy the parts separate and assemble one yourself; not rocket science to build one; there is a place in Cambridge (MA? England?) that sells on for <$100K; you can make a homemade one for ~$50K

Q7: how long will coating last?

At least 20 years; a guess, no hard evidence

One facet of this project is to build coatings even better than aluminum oxide

TERRY Weissman: lot of the current results presented here are theorhetical; we will be getting into more of the conservation issues as time goes along;

Also, we knew that NaOH would affect the copper; but often times, art objects are already Cu depleted; We might find a better solvent in the future

The focus of this presentation was to address problems associated with the use of slow and quick setting silicone rubbers for objects conservation applications. The main problem is that silicone rubbers often leave behind liquid and solid residues on objects after they are used. While it may be possible to physically remove the solids, the liquid residues often result in the development of a stain on the surface of the object where the silicone rubber had been applied. The question becomes, what is the chemical make up of these stains and can they be removed using solvents?

Why are we using these silicone polymers in the first place?
• to make casts for recasting
• to allow you to see an image or tool marks inscribed into a object better than you can see them on the object itself (silicone rubbers are homogeneous in color while objects themselves may not be)
• to non-invasively investigate the surface topography of the artifact

The research project entailed selecting eight different silicone rubbers and applying them to a series of different surfaces (plaster discs, limestone, and glass). Following removal of the silicones, attenuated reflectance-fourier transform infrared spectroscopy (ATR-FTIR) was used to determine the chemical make up (O-Si-O and Si-CH3 bonds) and depth of penetration of the liquid residues left behind. Several types of mass spectrometry (evolved gas, pyrolysis gas chromatography [PYGC-MS]) were used to study the eight rubbers and the molecular weights of the materials that are excreted out of the silicone rubbers and left on the different substrates.

RESULTS AND CONCLUSIONS:

* Hexane can be used to remove some of the staining material. I wasn’t sure how this conclusion was drawn? Regardless, it was a better solvent than either methanol (or was it ethanol) for removing some of the residue.

* When residues were observed, the color of residue was related to the color of the mold/silicome material

* Residues are mainly high molecular weight (HMW) components of the silicone rubber and are in their polymeric form – this wasn’t necessarily an expected outcome but it was what was observed

* It wasn’t possible to do a quantitative comparison of the amount of residue left behind between different rubbers

* Slow setting silicone rubber is bad for porous surfaces and residues can penetrate up to 100 microns into the surface (depending on the porosity of the object)

* Given the same rubber, the amount of residue left behind is a function of the material its applied to (intuitive?)

*Siloxane residues are comparable for quick setting rubbers

*Residues maybe reduced, but it is unlikely that they are effectively removed even with non-polar solvents

* There were a couple of others, but future work is to see if barrier coatings (methylcellulose) will help prevent residue deposition.

COMMENTS made following the presentation:

Baltimore museum stopped using silicone rubbers years ago; using silicones on rubbers causes patinas to disappear – patinas were saturated with silicone residues; little bits of set silicone were stuck in interstices of porous surfaces;

• I was surprised – atr is not really ideal for depth of penetration analysis; I also don’t think you can examine an area smaller than 20 um wide; can be hard to measure depths of penetration very accurately)

Any idea how porous the plaster is? Gypsum plaster – can you measure porosity?

Made sure used same batch of plaster throughout the experiments