How do you mount several tiny samples together?…..Very carefully!

We are all aware of how difficult it is to be able to take a sample from an artifact (both permission-wise and logistically) and when we need to, more often than not, the samples we take are extremely small.  Once we have our precious sample, we try to use as many examination and analytical techniques we can that are non-destructive to get the greatest amount of information from that one sample.  We may reach the point, however, where we need to use an analytical technique that may require the sample to be mounted, cut up or consumed, and we need to find ways to have the samples extend as far as possible through all the stages of investigation.

In our lab, we’ve been working on several projects (focusing on Egyptian blue pigments, as well as archaeological glass from the Mediterranean and China) that require taking very small samples from archaeological objects. Most of us are at the stage in our research that require the samples to be mounted in epoxy and polished for various types of instrumental analysis.  Because we can only take very small samples (about a few millimeters in size) and we need to use several techniques (SEM-EDS, EPMA, SIMS, Raman), we’ve been trying to figure out the best way to prepare our samples so that they can be used for all the techniques that will be applied.   Since the analytical methods we want to use will all work on polished samples mounted in resin blocks, we decided to try and mount the samples this way. In order to make it easier and faster to analyze several mounted samples, we decided to place several of our samples in the same resin block.  Arranging the samples all in one mount, documenting them in a way so you know which sample is which and embedding and polishing them successfully is challenging enough. When you are mounting 10-16 samples, about a few mm wide, in a 1 inch diameter sample holder, it’s even more difficult!

Before you start, it’s good to have all the supplies you need out  at your work area, along with your samples. Using a binocular microscope is key to mounting such small samples. The materials/supplies we had for mounting our samples were: the sample holder (we embedded our samples in 1 inch diameter disc of epoxy resin and used a Teflon ring -cut from a longer Teflon tube) as our sample holder, tweezers, double-sided tape (at least 1 inch wide) , Mylar (2-3 mil polyester film),  a pen and small, hard portable, surface for mounting (we used a small tile or piece of glass). Steady hands of course are essential.  No sneezing is allowed, and holding your breath for a bit  may also be helpful when dealing with such small samples.  Of course don’t forget to eventually breathe-just not on your samples!.

Once we had our supplies and samples at the microscope, we did the following:

1. We took our hard portable surface (in this case a small tile) and attached a piece of Mylar to the top of the tile using double sided tape.  The Mylar will act as a barrier and prevent the epoxy we use for mounting from adhering to the tile (if not it will be impossible to remove the mounted samples from the surface of the tile).
2. In the center of the Mylar covered tile, we placed 2 pieces of double sided tape, making sure the taped area was larger than 1 inch in diameter.  The tape will be used to hold the samples (and then the Teflon ring) in place during mounting.
3. We took the Teflon ring and placed it over the two pieces of tape and drew a line to mark the interior diameter.  This would help guide us in placing our samples on the tape, making sure they are positioned in the center of the ring.

 

Now it’s time to take your samples and place them on the double sided tape.  Since we’re going to mount several samples, we placed our in rows, and tried to position them so they would fall within the center of the Teflon ring when mounted.  We marked the top of the Mylar to indicate orientation.  We also took notes and made a drawing to map where we were positioning the samples. Because some of the analysis we will be conducting will require quantitative analysis and the use of standards, we mounted small samples taken from a set of Corning Museum glass standards (A-D) we had in the lab along side our archaeological samples.

Once we placed all our samples on the tape, we positioned the Teflon ring around them, on the guide lines we drew earlier.  Because the ring is made of Teflon, we don’t need to add any release agent because theepoxy resin won’t stick to it.

Now we’re ready to mix up and pour in the epoxy resin to embed the samples.  We use Struer’s Epofix epoxy resin for mounting.

Even though the Teflon ring is well adhered to the double sided tape, there is the possibility that some of the resin might leak out from the bottom edge of the ring.  One way to avoid this is to seal the bottom edge of the Teflon ring.

A couple things we’ve tried are:

• putting tape along the bottom exterior edge of the Teflon ring  (in the image above we used blue masking tape)
• putting plasticine or modeling clay along the bottom edge
• or sealing the exterior bottom edge with latex (This is the one that worked best for me.  I brushed Latex #74 molding compound from Douglas and Sturgess around the bottom edge.  Once the latex was set, I mixed together the epoxy resin and poured it into the ring and….no leaks!)

When embedding our samples in resin, we like to put them in a vacuum chamber after pouring in the epoxy to remove any air from the resin and the pores of our samples.  This will ensure the samples are completely impregnated with epoxy.  This is particularly important with porous samples, such as some of the very weathered glass samples I was going to analyze.

    

After the epoxy cures, the pressure is released from the vacuum and the tile/ring/mounted samples removed.

The Teflon ring can now be lifted off the Mylar and the mounted samples removed from the ring.  The final step is to polish the samples.We start off with very fine grit sand paper (ranging from 600-1200 grit) and finish with Buehler MetaDi Diamond polishing suspension, first with 6 micron suspension followed by polishing with the 1 micron suspension as the final step. We want to make sure that the samples are exposed and that there are no scratches on the surface.

Once the mounted samples are polished, they are ready to be analyzed.

 

Having to mount numerous small samples together is tricky, but having all these samples in the same mount, plus the standards, will certainly save time during analysis!

Vanessa Muros (Conservation Specialist)

UCLA/Getty Program Welcomes Visiting Scholar Dr. Xiaoqi Wang

The UCLA/Getty Program is pleased to welcome visiting scholar Dr. Xiaoqi Wang for the 2013-14 academic year. Dr. Wang received her Ph.D. at the University of Science and Technology of China in conservation science and archaeometry (2005). Her dissertation research focused on the conservation of ancient shipwrecks and waterlogged materials with work undertaken in the conservation lab of the Romano-Germanic Central Museum, Mainz, Germany. Xiaoqi was a postdoctoral fellow (2006-2012) at Nanjing University in geophysics performing archaeometric research on Chinese archaeological glass beads and pigments dating between 220B.C.-600A.D. She serves as the Research Fellow in Department of Archaeology at Nanjing University, where she has also been teaching archaeology undergraduate and graduate students about archaeometry and conservation science since 2005. She was a visiting scholar at the University of Vienna, Austria (2001) and the Romano-Germanic Central Museum (2004-2005), made possible with funding from the University of Vienna and Romano-Germanic Central Museum respectively

During her time here, Dr. Wang will be working with UCLA/Getty Program chair Dr. Ioanna Kakoulli, as well as other colleagues in the UCLA/Getty Conservation Program and the Cotsen Institute of Archaeology. She will continue her research on beads and pigments focusing on the use of LA-ICP-MS, lead isotopic analysis and microscopy for their analysis. She is also focusing on ancient Chinese scroll paintings and hopes to connect with conservators, scientists and scholars on the identification of deterioration issues and solutions for preserving the paintings.

Student Class Projects Focus on Technical Examinations of Cultural Materials

In the fall of 2009, the UCLA/Getty Conservation Program offered the course “Introduction to Archaeological Materials Science: Scientific Techniques, Methodologies and Interpretation” (CAEM M210) that focused on basic scientific techniques employed for the examination of archaeological and cultural artifacts to answer questions of anthropological significance and their state of preservation. Among the techniques covered were UV/VIS/NIR spectrophotometry, X-ray fluorescence (XRF), X-ray diffraction (XRD), scanning electron microscopy and energy dispersive spectroscopy (SEM-EDS), and Fourier Transform Infrared Spectroscopy (FTIR). Students were assigned small research projects in which they would apply these techniques, in addition to others discussed in this and other courses, to the investigation of various materials to answer questions about technology and condition.

The four groups of artifacts studied were:

• samples of a Byzantine wall painting from St. Neophytos, Cyprus
• samples of fibers associated with a mummy bundle excavated by the Tarapaca Valley Archaeological Project in Chile
• glazed ceramic sherds from the American Southwest
• 2 Balinese paintings on canvas belonging to the Fowler Museum at UCLA

At the end of the term, the students presented their poster, which was displayed at the Cotsen Institute of Archaeology. Below are two of the posters produced as the final project for the class.

Make sure to stay tuned to this blog for upcoming posts on the other posters presented, as well as future student projects.

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Investigation of Pigment Alteration in the Wall Paintings at the Enkleistra of St. Neophytos, Paphos, Cyprus
Steven Brightup, Sara Kiani, Nicole Ledoux, James Ma, Saurabh Sharma

Project Summary
A series of 5 blue and 5 red pigment samples from the Enkleistra of St. Neophytos, the place of reclusion, in Paphos, Cyprus were analyzed to determine the pigments identity and possible alteration products. Fourier Transform Infrared Spectroscopy (FTIR), Variable Pressure Scanning Electron Microscopy – Energy Dispersive X-ray Spectroscopy (VPSEM-EDS), Polarized Light Microscope (PLM), and Binocular (stereo) Microscope (BM) were used to analyze the samples and due to the limitations of the techniques, only inconclusive assignments can be made on the pigments’ identity.

From elemental analysis it is suspected that the blue pigment is lapis lazuli and that there are two different red pigments which are cinnabar HgS and red lead (Pb₃O₄). However, without phase analysis of these samples, a positive identification cannot be made. Alteration of red to black and dark blue to light blue were observed for the samples analyzed. A possible alteration of Cinnabar is to metacinnabar. Documented alteration products of red lead are to plattnerite [β-PbO₂] and anglesite [PbSO₄]. Fading of lapis lazuli has been attributed to the breakdown of the Al-O-Si in the literature. However, it was not possible to verify if these are the alteration products with the available tools.

The Identification of Fibers from a Mummy Bundle, Tarapaca Valley, Chile
Tessa de Alarcon, Elizabeth Drolet, Robin O’Hern and Cindy Lee Scott

Abstract
Fiber samples from a formative period mummy bundle from Tarapaca 40 in the Atacama desert of Chile were examined in an attempt to identify
them. Standards of human hair and alpaca were used for comparison. Fourier transform infrared spectroscopy (FT-IR) spectra were collected on the samples and standards. The morphology of the fibers and standards were examined using polarized light microscopy (PLM), scale casts and cross-sections. The spectra from the FT-IR analysis could not be used to differentiation between human and alpaca hair. Based on morphology, three samples were identified as camelid and two were tentatively identified as human.

Technical Study of Two Japanese Masks: Investigating Their Attribution as a Pair

The work described in this poster was conducted as part of a Master’s thesis project for the UCLA/Getty Conservation Program and presented at the Annual Conference of the Association of North American Graduate Programs in Conservation (ANAGPIC), Buffalo State College, April 24-25, 2009.

The Fowler Museum at UCLA houses a collection of Japanese polychrome wooden masks. A pair of these masks, identified as “honomen” (gift or dedication mask), was attributed to the same maker based on their stylistic similarities. The museum records stated that the masks were dated to the 18-19th century and made in the style found in the Kyūshū region of Japan. However, neither the pairing nor provenance of the masks was supported by any textual or technical evidence.

The poster presented here summarizes the preliminary results from a comparative technical investigation on the Fowler masks, as a part of the research to answer the questions regarding the masks’ provenance and their paired attribution. Analytical techniques such as wood characterization, polarized light microscopy (PLM), x-ray fluorescence spectroscopy (XRF), x ray diffraction (XRD), gas chromatography-mass spectrometry (GC-MS), pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) and micro-chemical analysis using environmental scanning electron microscopy (ESEM-EDX) were used to determine the masks’ material composition and methods of manufacture. The analytical results, combined with studies on the masks’ context of use and iconographic origins, provided material evidence that the masks were manufactured in close association with one another, although there was no firm evidence to establish that they were indeed manufactured by the same hand. Furthermore, identifying vitreous pigments on one of the masks pushed the mask’s estimated date of manufacture to 19th-20th century. This finding also added knowledge to a class of pigment not widely used in the Japanese palette until modern times.

Built upon the analytical understanding of the Fowler masks’ material composition and present condition, the research project concluded with a conservation treatment to improve the long-term stability of the polychrome. The most urgent treatment priorities were stabilizing the fragile matte paint surface and locally reinforcing the structural defects on the masks. Due to time constraints, consolidation of the paint was performed only on the red mask. Major structural defects on both masks were reinforced by filling the cavities in the wood with a light-weight and mechanically-reversible fill made of rolled-up Japanese paper, capped with a light-weight putty made from Acryloid B-72 bulked with glass microballoons for a better seal. The fill was then inpainted with Liquitex acrylic emulsion paint to reduce the color contrast between the fill and the wood.