The Conquistador’s Coat: Characterization of a surface coating on a Guatemalan polychrome mask

This past spring quarter, for the course “Conservation Laboratory: Organics III”  (CAEM 241), I had the opportunity to examine and treat a polychrome mask (X91.470) from the collection of the Fowler Museum at UCLA.  The polychrome mask is made of carved wood  and is  likely meant to depict the face of a conquistador, with detailed curling hair, a long beard and mustache, and a light complexioned, pink face.

Masks such as this one are commonly used in ceremonial dances in Guatemala, and one such as this may have been used in the Dance of the Conquest, a dramatic dance that depicts the Conquest of Guatemala by the Spanish in 1524 (Pieper 1988: 39) . You can see a portion of this dance in this YouTube video, where several of the dancers are wearing a mask similar in appearance to the Fowler conquistador mask.

The mask is painted with thick layers of paint that are currently heavily obscured by a thick accumulation of soiling that is likely on top of a discolored surface coating. Guatemalan dance masks are traditionally professionally maintained by costume shops called morerias, which apply fresh paint to keep them looking new.  The age of the mask is not necessarily considered a marker of value, and it is actually preferred that the masks look new and well maintained when they are danced.  Some masks may be blessed by an indigenous Shaman or Catholic priest (Pieper 2006: 43-45) .  Historic accounts of the maintenance of these masks do not refer to the application of any surface coatings as a protective measure for the polychromy.

Description of the coating

The majority of the painted surface of the mask is obscured by a thick layer of a dark, grimy material with embedded soiling (fig. 1-2).  It is unknown when or for what purpose the coating was applied to the mask, but it may have been applied for surface protection of the polychrome or to consolidate flaking paint.

Figures 1 and 2. An image of the front of the Conquistador’s mask (X91.470) (left) with a detail (right) of the area of the nose showing the discolored surface coating.

Under stereo binocular magnification (7-45x), the material has a varied appearance, at times appearing like a matte coating that is heavily embedded with soiling of a granular nature (fig. 3), at times flaking (fig. 4), and in other instances appearing thinner, with a somewhat sticky texture, but less accumulated matte material (fig. 5).

Figure 3. Soiling on the mask that is granular in nature

Figure 4. Dark surface material that is flaking.

Figure 5. Some of the dark material on the surface appeared thinner and sticky, and some areas had a matte appearance.

There are also areas where the surface coating has a wrinkled appearance, as if it has shrunk and pulled away from the surface, and in these cases it appears to be pulling the paint layer with it (fig. 6).  The wrinkled areas look the way that paint looks when a commercial paint stripper is applied.  In all of its iterations, it appears to be inextricably linked with flaking paint layers beneath it (fig. 7).

Figures 6 and 7. In some areas the surface coating appears as if it shrunk and pulled away (left). Regardless of the appearance or texture of this coating it is inextricably linked with flaking paint layers (right).

There are a few areas where the obscuring dark coating is not as present.  In these areas, it appears that there may have been an attempt to remove it, which resulted in peeling away of the top paint layer as well (fig. 8a and b).  In these instances, the pink paint film has been pulled away and is folded over onto the surface of the mask and adhered in place. The areas of folded paint film appear to be brittle and have shattered in some locations along the edges.  There is a sticky, light brown resinous material that has accumulated in the crevices of these surfaces, which is likely deposited residue from the surface coating. In addition, a distinct layer of soiling has accumulated on top of the coating.  Much of the soiling appears embedded within the coating, but there is also loose surface dirt that can be moved with a soft brush.

Figures 8a and b. In some areas, it appears as if there was an attempt to remove the coating (left) which resulted in peeling away of the top paint layer (right).

UV Examination

The object was illuminated with ultraviolet radiation at λ_excmax=300-400nm and captured with a Nikon D90 digital camera affixed with the PECA 916 filter (visible range). The soiled coating that covers the face appears largely absorbing.  Areas of fluorescence occur where the flesh colored paint is exposed without the coating (fig. 9).

Figure 9. Under examination with a UV light (λexcmax=300-400nm) the soiled coating appears largely absorbing. Areas of fluorescence occur where the flesh colored paint is exposed without the coating.

Solubility Testing

Solubility testing was conducted in situ on the mask with room temperature deionized water, warm deionized water, acetone, ethanol, toluene, and mineral spirits.  The coating was unresponsive to cool water, acetone, ethanol and mineral spirits, but a slight change in appearance was noticed when toluene was applied, though none of the coating was removed onto the swab.  This surface change was fleeting and the coating returned to its original appearance immediately.  Just to be certain that the coating was insoluble in toluene, the application of toluene on a small sample of coating that had flaked off of the surface was observed under stereo binocular magnification at magnifications of 7-45x.  No dissolution or swelling of the coating material was observed (fig. 10).

Figure 10. No dissolution or swelling of the coating material was observed in toluene.

The mask was undergoing treatment because the painted surface was unstable and was lifting and flaking.  Gelatin was under consideration as a consolidant for the flaking paint and therefore warm water was also tested to ensure that a warmed gelatin solution could be used without disrupting the appearance of the coating.  Unfortunately the warm water was found to swell and eventually solubilize the coating so that it could be swabbed away with gentle pressure.  The interaction of the coating with warm water was further investigated by observation under stereo binocular magnification.  As the sample soaked in the warm water the brown material on the sample surface swelled into fluffy blobs on top of a more transparent, clear base.  Over a period of time the clear, striated section of the sample also appeared to swell slightly (fig. 11).  Because warm water was observed to have an effect on the coating, a small cleaning test was conducted in a discreet area of the mask using warm deionized water applied by swab under stereo binocular magnification.  The coating was greatly reduced using this method and it is very likely possible that it could be removed simply using warm water, if removal were desired.  Though the solubility in warm water introduced a possible complication with using a warm, aqueous consolidant such as gelatin, the fact that the gelatin would remain soluble in water was also a possible advantage to using this consolidant; should the removal of the consolidant be desired in the future, it would be beneficial if it was not consolidated in place with a system using toluene (the only solvent besides water that did not affect the paint layers below) for toxicity reasons.

Figure 11. Swelling of the coating was observed in warm water.

Additional Microscopic Observations

Two small samples of the pink paint was removed from a discreet area of the mask where the paint layer contained a layer of the dark coating and was observed to be flaking.  This flake was viewed in transmitted light using an Olympus BX-51, polarized light microscope at magnifications between 50-200X.  Using this technique, it was not possible to observe the layers as distinct entities, however, at the edge of the paint flake and within interstices of the flake, small sections of the coating could be observed.  It appeared to have a somewhat clear and amorphous structure (fig. 12a and b).

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Figures 12 a and b. Examination of a paint flake with the coating viewed under transmitted light.

In addition, several small samples of the coating were removed from the mask during a light surface cleaning procedure.  These samples were soaked in warm water as described above, in order to further characterize the solubility of the material.  These samples were viewed in transmitted light under high magnification and also in cross-polarized light. (fig. 13a and b) The samples appeared to swell from exposure to the water.  The material was quite clear, and had the appearance of an organized cellular structure in some areas.

Figures 13a and b. Examination of the coating using transmitted (left) and cross-polarized light (right) after swelling in warm water.

Spot testing

Two microchemical tests were conducted in the hope of possible identification of materials present: a test for polyamides using p-dimethylaminobenzaldehyde (Odegaard et al. 2000: 170-171), and a test for protein using copper (II) sulfate (Odegaard et al. 2000: 144-145).

The test for polyamides was conducted to confirm or deny the presence of nylon, had the mask been treated with soluble nylon (N-methoxymethyl nylon, a chemically modified form of nylon that is produced by treating nylon with formaldehyde). Soluble nylone was a common consolidative conservation treatment for powdering or flaking paint beginning in the late 1950s.  Objects that have undergone treatment with soluble nylon have been observed over time to exhibit numerous problems including accumulation of disfiguring and obscuring soiling in the nylon film, the film exerting strong contractile forces which peel away surface layers from objects, and the film losing flexibility and becoming insoluble (Sease 1981).  These descriptions of the degradation characteristics of soluble nylon in the literature were similar to the appearance of the coating on the Fowler mask. Neither the age of the mask nor its conservation history are known, and it was possible it could have been treated at a time when soluble nylon was a popular conservation treatment. The result of the spot test was negative and was compared to a known positive result (color change to red of filter paper used in the test) from a nylon sample taken from the ResinKit™.

The protein test was conducted because of the coating’s swelling effect in warm water.  In addition, from the literature it is known that at high RH levels animal glue films can experience severe shrinkage due to contraction of the glue matrix, and in some instances the coating appears to be undergoing contractile shrinkage as described (Schellmann 2007).  The result of the protein test was negative and was compared to a known positive sample of gelatin.

Conclusion

Based on the above observations and testing, the material constituents of the coating could not be identified.  Nylon-based (such as soluble nylon) and protein-based (such as animal glue) coatings were ruled out based on the spot testing results.  Knowing that the material is soluble in warm water is important information should the removal of the coating be desired in the future.  At this time, because the nature and purpose of the coating have not been identified, its removal would not be an appropriate course of action, so it will be left intact.  An additional problem posed by the presence of the coating is that the paint layers below it are flaking, and the coating may be contributing to or in fact causing the flaking.  In order to consolidate the paint layers below without removing the coating first, the coating and accumulated soiling also become consolidated as a result.  Even though warm water has the ability to swell or solubilize the coating, mechanical action is also required to remove it.

Though the warmed consolidant did have the potential to interact with the coating, care was taken to only flow the gelatin under lifting or detaching paint flakes and to try to avoid saturating the coating with consolidant.  This worked rather well in the areas of pink polychromy.  When cleaning was required around the consolidation site, this was done immediately, and the coating was not affected.  In the areas of the hair and beard, the nature of the coating was somewhat different, as described above (fig. 4).  When this iteration of the coating came into contact with the warm gelatin, it solubilized quite easily.  Again the focus of the treatment was consolidation of localized areas of active flaking or evident wood deterioration, and care was taken in choosing sites in which to introduce the consolidant by brush without disrupting the coating.  When the consolidant was applied with care under binocular magnification, the coating was not at risk of being removed.  Furthermore, by using this aqueous consolidant, the solubility of the coating in warm water should not be affected, should its future removal be desired.

References

Odegaard, Nancy, Scott Carroll, and Werner S. Zimmt. Material characterization tests for objects of art and archaeology. Archetype, 2000.

Pieper, Jeanne, and Jim Pieper. Guatemalan Masks: The Pieper Collection. Craft and Folk Art Museum, 1988.

Pieper, Jim. Guatemala’s Masks and Drama. University of New Mexico Press, 2006.

Schellmann, Nanke C. “Animal glues: a review of their key properties relevant to conservation.” Studies in Conservation 52, no. Supplement-1 (2007): 55-66.

Sease, Catherine. “The case against using soluble nylon in conservation work.” Studies in Conservation 26, no. 3 (1981): 102-110.

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Written by Lesley Day (’16)

Investigating Adhesives Used for Mending Leather

The UCLA/Getty Conservation students investigated adhesives for leather this past Tuesday as a practicum, taught by Andrew W. Mellon Resident in Conservation Education Tharron Bloomfield, for their Deterioration and Conservation of Organic Materials III course (CAEM 241). Students divided themselves into three groups each with a different set of adhesives and application methods to test. All groups worked with oil-tanned leather scraps (chamois) on which they created their own rips, cuts, or tears. Each group also worked with four carriers for the adhesives: Hollytex, Reemay, Japanese tissue paper, and Goldbeater’s skin. Heat spatulas were used to apply the heat set adhesives.

One group working with Beva 371 film tested different methods for applying the film to the carrier and the mend. They also investigated the application of Beva at different temperatures and the strength each mend created. Through testing, they realized their preference for using a two-step application for the repair, where the Beva is heat set onto a carrier, which is then heat set onto the damaged area.

Carrine Tzadik, Alexis North, and Brittany Dolph (L to R) evaluate the process of heat setting Beva film to different carriers.

Another group focused on Lascaux 360HV, Lascaux 498HV, and a 1:1 combination of the two adhesives  They tested the performance with immediate tack and painting the adhesive into a film with one or multiple coats, and then heat setting. This group had varying opinions about the effectiveness of some of the carriers. Some liked the smooth texture of Reemay and felt that mends using this carrier were structurally sound while others thought it needed too much application of heat to set.  In one case, this group saw significant damage to the leather substrate due to too high of a temperature used during the heat application, causing changes in the physical properties of the leather.

Madeleine Neiman, Ayesha Fuentes, Tharron Bloomfield and Geneva Griswold (L to R) compare different application methods for applying Lascaux 360HV and Lascaux 498HV

A third group worked individually on applications of Paraloid F-10 in mineral spirits and 48% PVAc AYAF in acetone for patch mends and bridge mends. They tested various methods of solvent setting as well as heat setting. They had a visual preference for the mends with Goldbeater’s skin and saw damage in the form of tidelines and darkening to the leather in the use of the solvents to set the adhesive.

An example of the testing conducted by Caitlin Mahony in the group investing PVAc AYAF and Acryloid F-10. Other group member Casey Mallinckrodt also developed her own system of testing the mends.

At the end of the practicum, students felt more informed about adhesive options for leather and are ready to begin treatment on their leather objects from the Fowler Museum this quarter.

Caitlin Mahony (’14)

Powdery Paint Consolidation Part I: Setting up an Ultrasonic Humidifier and Nebulizer

…or more aptly titled “The trials and tribulations of how to set up this equipment and only get two seconds of a consolidation mist before it all goes wrong”.

And no, that isn’t too much of an exaggeration. As useful as the application of a consolidant mist is for the treatment of powdery or unbound paint, we have found that the set up of the equipment can be difficult, and getting it to actually work can be hit or miss. There seem to be a lot of components to the systems—with connectors and tubing providing areas for leaks and many locations where things can go wrong. Though some images or diagrams in the literature describe the “proper” set up, it still seems that the systems are a little tricky to set up and do not always work consistently (if at all!). We recently set up these misting systems for a lab the conservation program students undertook on the consolidation of powdery paint for the course on the Deterioration and Conservation of Organic Materials III (CAEM241), and we thought it might be helpful to share how we set up our equipment, some of our discoveries along the way, and the issues we encountered.

For those of you not familiar with this type of consolidation, in which the consolidant is atomized or aerosolized, it can be preferable to other methods of application because small quantities of consolidant can be applied as extremely fine particles in a controllable flow. This is especially helpful for paints that are unbound or underbound (such as matte, powdery paints often found on Oceanic and African artifacts), as it provides a low impact method of application. To achieve this, you can use an ultrasonic humidifier, aerosol generator, a nebulizer or some other type of equipment to create a mist that is then applied to the area of powdery paint you want to consolidate. Ultrasonic misting allows for very fine droplets (about 1-10 microns) to be delivered in an airstream saturated with solvent positioned close to the surface (therefore the solvent evaporates very minimally); this offers an advantage over pneumatic sprays, which may evaporate in the air before reaching the object, becoming too viscous to properly penetrate the paint (Michalski, et al. 1994).

Detail of wooden object with powdery paint on the surface

Problems that are usually associated with consolidation of powdery pigments (darkening, glossy appearance, smearing), are often due to the fact that too much consolidant is being used at concentrations that are too high, while ultrasonic misting can avoid both of these problems. Misting requires the use of very dilute solutions, allowing for a weak consolidant to be applied to a relatively broad area. This form of application also allows the treatment to be carefully assessed as it progresses, so that the consolidation may be stopped before any noticeable darkening or other alterations to the surface occurs. As we will see, the use of the ultrasonic humidifier, the nebulizer or the aerosol generator involves a relatively complex set up, which can create a number of challenges.

And so the saga begins…
If your lab is lucky enough to have something like the AGS 2000 HS aerosol generator from Lascaux, then you don’t have to worry about any kind of set up. This piece of equipment is ready to use and does not require additional equipment or components (or “jerry-rigging”). However, the aerosol generator is expensive and it developed after conservators implemented alternative systems employing an ultrasonic humidifier or nebulizer to produce a mist for consolidation. For this particular class, we had the students work with the aerosol generator, but we also wanted them to use the other two systems since those would likely be the types they would encounter at other institutions or even have to set up themselves.

Elizabeth Drolet uses the aerosol generator to consolidate powdery paint.

The ultrasonic humidifier – The day starts off on somewhat of a high note
The first system we set up was with the ultrasonic humidifier. Luckily for us, there are some good published diagrams of how it needs to be assembled (Cavanaugh 2001 ; Dignard, et al. 1997). The system consists of an ultrasonic humidifier, an aquarium pump to provide pressurized air, an LDPE (low density polyethylene) bottle into which you place your consolidant, and tubing. This method is relatively inexpensive. You only need a household ultrasonic humidifier and an air pump or compressor. We used a small aquarium pump, the Optima Maxima A-806 pump with a rheostat, as our air source.

We cut two holes into the LDPE bottle, as illustrated in the diagrams from the referenced articles, and inserted two pieces of tubing, held in place with EVA (ethylene vinyl acetate) low melt, hot glue. One piece of tubing was connected to the aquarium pump and the other piece of tubing acted as the nozzle for the delivery of the consolidant. We wanted to create a fine tip at the end of the delivery tube for the application of the consolidant, so we cut the end off of a plastic disposable pipette and inserted it over the end of the tubing.

The LDPE bottle was positioned just above the oscillator of the humidifier and held in place using a small lab stand. We didn’t place the bottle directly on the oscillator because in the past contact with the oscillator caused the bottom of the bottle to melt. We then filled the humidifier reservoir with water.

Our ultrasonic humidifier set-up

Now it was time to add our consolidant. For initial set up and testing of the system we just used deionized water to act as our trial “consolidant”. When we added our “consolidant” to the LDPE bottle, we made sure that the level of the trial “consolidant” did not go above the water level of the reservoir.

So we set everything up, turned on the aquarium pump, then turned on the humidifier, and….SUCCESS!! We got mist!

Okay, okay, it wasn’t that easy. We left out some of the problems we encountered with setting it up.

• Not all humidifiers are the same or seemed to work
  We had two humidifiers in the lab: a Holmes brand ultrasonic humidifier and a Sunbeam ultrasonic humidifier that we use for the Preservation Pencil. For some reason we could not get the Sunbeam humidifier to produce a mist using this set up, even though it works as a humidifier. We aren’t really sure why this happened. We did notice when looking at the two humidifiers that the oscillator and surrounding plastic disc of the Sunbeam humidifier is smaller in diameter than the one in the Holmes humidifier (1.7cm in diameter as opposed to the 4cm oscillator and surrounding plastic disc on the Holmes humidifier). For now our theory is that the smaller Sunbeam humidifier’s oscillator is not powerful enough to produce a mist, but we aren’t exactly sure what is going on.

• The length of the tubing used to deliver your consolidant makes a difference
  If the consolidant delivery tube was too long, we did not seem to get any misting. We thought this could be because our aquarium pump was not powerful enough to push the air/mist through such a long tube. If the tube was too short, we would get more unwanted droplets of consolidant coming out of the nozzle, and in some cases these were pushed out of the tube with some force by the air pressure. The amount of air flowing through the tubing and the intensity of the oscillation also affected how much liquid consolidant was pushed through the end of the nozzle.  We found that adjusting the rheostat on both the aquarium pump and the humidifier helped mitigate this.

The nebulizer – Where things got frustrating and started to go wrong (and when Teflon tape became our best friend)

Feeling pretty confident from our successful set up of the ultrasonic humidifier, we started to work on putting together the nebulizer. It has fewer components to the system so we thought it should be a piece of cake—or not—as we were soon to learn.

For the application of a nebulizer for consolidation, some treatments have involved the use of a medical nebulizer (Grantham and Cummings 2002) which again, like the aerosol generator, comes ready to use. In our case we were going to assemble our own nebulizer system using a nebulizer cup (which is where you place the consolidant) and a source of compressed air (using the aquarium pump).

The nebulizer cups we bought have two openings: a side arm to attach the tubing for the air and a hole on the lid of the cup where we attach tubing to deliver the consolidant. We used some silicone tubing that came with the aquarium pump to connect the pump to the nebulizer’s side arm. We then used clear tubing and attached it to the opening on the top of the nebulizer using polypropylene connector/reducer nozzles purchased from a lab supplier. We once again cut the tip off of a plastic disposable pipette and inserted it at the end of the tubing as our nozzle.

The nebulizer attached to the aquarium pump

With everything connected, we filled the nebulizer with water, turned on the aquarium pump and waited…and waited….and kept waiting…but there was no mist. We talked to a colleague (who had successfully used a nebulizer for mist consolidation) who said that we needed to make sure there were no air leaks anywhere. So we grabbed our Teflon tape and wrapped it everywhere there was a connection to ensure all the parts fit together tightly with no air leaks. She also mentioned that she filled the nebulizer cup half way with consolidant, which seemed to be the right amount to get the mist to form for her. So we filled our cups half way with deionized water, but still got nothing.

We then noticed that the solution in the cup did not seem to be aerosolizing or moving much at all and we could only feel a small amount of air coming out of the tube. We wondered if this was caused by the length of the tubing we were using, like with the ultrasonic humidifier, but shortening or lengthening the tubing either from the pump to the nebulizer or for solvent delivery did not make a difference.

Our next idea was that the aquarium pump we were using did not have enough pressure to produce a mist. The Optima Maxima A-806 pump works at a maximum pressure of 2.5 psi (pounds per square inch). We tried a compressor we had for our air brush which has an operating pressure of 20-40 psi. We connected the nebulizer to it, turned it on and immediately produced a mist!

The nebulizer connected to the air brush compressor (20-40 psi)

We noticed, however, that there was a very strong flow of air coming out of the delivery nozzle. When we tried to “consolidate” a facsimile with flaking paint, the air coming out of the nozzle blew the paint flakes off of the surface. The compressor seemed to be too powerful.  This meant we had to find a compressor that was stronger than the small aquarium pump but not too strong to blow the fragile paint off the surface of an object. We settled on a slighter larger aquarium pump with a psi of 4 (the Optima Maxima pump A-407) and that seemed to work well in producing a mist.

The nebulizer when attached to the air brush compressor produced too strong of an air flow which blew off flakes of paint from the facsimile tested.

In addition to the difficulties with trying to find the right air compressor to produce the mist, we also had some issues with the length of the consolidant delivery tube. We wanted the tube length of the delivery nozzle to be long so we would not have to hold the nebulizer cup in our hand while conducting the treatment and instead could leave it on the table. However, we found that if the tube was too long, no mist was produced. Therefore, we had to settle for a shorter tube length for the delivery nozzle, which meant holding the nebulizer cup over or right next to the object while consolidating it.

Cindy Lee Scott tries out the nebulilzer. Because the tube for the delivery nozzle had to be short in order for the mist consolidation to work, the nebulizer cup had to be held close to the object (or over it) during treatment.

After a couple of days of setting up and trying to get the nebulizer and ultrasonic humidifier to work successfully with water, we were ready to try the mist consolidation on facsimiles with powdery paint, using actual consolidants. Stay tuned for part II of this post, which will discuss how those treatments went and the issues we encountered.

References

Cavanaugh, Jan.  2001.  The Feasibility of Ultrasonic Misting as an Inpainting Technique.  WAAC Newsletter.  Vol. 23, No. 1 (January).

Dignard, Carole, Robyn Douglas, Sherry Guild, Anne Maheux, and Wanda McWilliams. 1997. Ultrasonic Misting, Part 2, Treatment Applications. Journal of the American Institute for Conservation 36(2): 127-141.

Grantham, S. and A. Cummings. 2002. “Painted Japanese paper screens: the consolidation of paint layers on a paper substrate. In The broad spectrum: studies in the materials, techniques, and conservation of color on paper, eds. H.K. Stratis and B. Salvesen. London: Archetype Publications.

Michalski, Stefan, Carole Dignard, Lort van Handel, and David Arnold. 1994. The Ultrasonic Mister: Applications in the Consolidation of Powdery Paint on Wooden Artifacts. In Painted Wood: History and Conservation, Proceedings of a symposium organized by the Wooden Artifacts Group of the American Institute for Conservation of Historic and Artistic Works and the Foundation of the AIC, held at the Colonial Williamsburg Foundation, ed. V. Dorge and F. C. Howlett. Los Angeles: The Getty Conservation Institute, 1-18.

Vanessa Muros (Staff Research Associate), Dawn Lohnas (’12) , and Ellen Pearlstein (Assoc. Professor UCLA/Getty Program and Information Studies)