Posts Tagged ‘testing’

Conservators at the Alaska State Museum are regularly asked this question:

“What’s that white stuff?”

Disfiguring white stuff on artifacts and artworks can be the result of a wide range of causes. These are referred to by a variety of terms including: efflorescence, bloom, fatty bloom, spue, blushing, chalking, blanching, haze, dust, grime, salts, mold, transferred images, crizzling, sweating and patina. While these terms each refer to specific types of damages and disfigurements, they are often used interchangeably. This may be due to the similar appearance many of them have at first glance. White fuzzy material on an artifact is often assumed to be some type of mold. Sometimes this is the case, but a number of other things can have the same appearance. Staff at the Sheldon Jackson Museum were concerned that Tlingit hide armor was breaking out with mold. Small white fuzzy patches were disfiguring the surface, and the problem seemed to be getting worse. However, upon examination, the white substance was waxy and records indicated a leather dressing treatment was undertaken in the late 1960’s. At the time, leather dressings were a common part of museum practice and believed to benefit leather by aiding flexibility. Over time, the fats can alter and come out of the leather as a bloom or spue, disfiguring the surface. Leather dressings are no longer part of museum conservation practice.

A wooden dish in the Alaska State Museum collection has a fine sugary-looking white deposit inside. Examination and history of the dish reveal the crystals are related to the bowl’s history as a vessel for holding grease or oil. The presence of those crystals is part of the history of the artifact and tells a story.

GETTING STARTED

“What’s that white stuff” is a great question. Does it belong there? Is it hazardous to humans? Is it destroying the artifact? We suggest a systematic approach to the problem.

  1. Identify the material affected. What is your artifact made of? Our INDEX lists artifact materials vulnerable to “white stuff.”
  2. Examine the context and history of the artifact. What was it used for? How was it maintained? Was it dug out of the ground? Has the environment been stable? Has it been on exhibit? Also ask folks who have worked at your museum a long time. These clues may help narrow down possibilities. Write them down.
  3. Characterize the appearance of the white stuff. Is it powdery? Sticky? Flaky? Is it a haze or a crust? Does it appear in a pattern? Use our list of descriptive words below to help you. Write it down. Take a photo for the files.
  4. Consider the typical POSSIBILITIES. For each kind of material, there are certain kinds of white stuff that we have see more than others in Alaskan collections. We try to list these in the INDEX by material.
  5. Test the hypothesis. Make a guess at what you think it is, and if you can remove a little bit, test your theory.

HOW DO I DESCRIBE WHAT I SEE?

Here’s a list of vocabulary words that can help you characterize what you are looking at.  These words, plus a photo, can help others work on solving your mystery. Check GLOSSARY if needed.

airy

branched

chalky

cloudy

crumbly

crusty

crystalline

dotted

dry

fibrous

filmy

foamy

fuzzy

glossy

grainy

greasy

hard

hazy

matte

opaque

powdery

rough

spidery

spotty

sticky

soft

sugary

translucent

HOW CAN I ANALYZE MY WHITE STUFF?

EASY

  1. Magnifying glass and strong light. Look carefully at the surface and try to characterize the appearance. Is it an optical effect from delamination or abrasion? Or is it accumulated on the surface, indicating an accretion or efflorescence?
  2. Does it roll easily on a tipped surface, like tiny dry balls?  You may have insect frass.
  3. Look for patterns on the surface or an explanation for why the white stuff is in some areas and not others. Consider different materials, which side is “up” and if the pattern may be associated with something applied as a liquid.
  4. If you can sample it with a small pointy tool, note how difficult it is to remove. Powdery? Crumbly? Sticky? Smeary?  This is an important clue. Don’t remove it all during sampling, you may want to try again with another idea.
  5. If you have removed a bit of it, try rubbing some of it on a clean glass surface. Does it smear? Or does it stay crumbly/powdery? A smearing substance can indicate the presences of fats or waxes and may indicate the sample is some type of fatty bloom.
  6. Try adding a drop or two of water, enough to cover the sample. Does it dissolve? If so, it may be a water-soluble salt.
  7. With another sample, try adding a drop or two of mineral spirits.  Does it dissolve now?  Perhaps it is something waxy.
  8. If the sample melts with gentle heating, it may be a wax or bloom. Melting can be done over a hotplate, or even with a bit of foil over a candle.

TRICKY:

  1. If you have a binocular microscope, you can see more detail. For example, branching structures of mold may be visible. Crystals may be evident. Bug parts are more obvious under magnification.
  2. If you have a polarized light microscope, you can see even more detail and observe optical properties. Fruiting bodies confirming mold may be present.

HARD:

  1. Various kind of instrumental analysis may be available at larger museums or universities.  For example, an XRF can identify certain heavier elements that point to specific possibilities like metal corrosion, pesticides etc.
  2. If you are equipped to use acids safely, add a couple of drops of HCl. If your sample bubbles vigorously, it may be a carbonate. Maritime accretions and insoluble archaeological salts often bubble with this test.
  3. While some resources may suggest tasting the salt to confirm that is what it is…this is not a good idea and tasting should never be done to identify an unknown substance. The salts forms in Byne’s disease, for example, are not components of common table salt (sodium chloride) and should not be consumed.
  4. Spot testing can help characterize “white stuff” but you must be equipped with a chemistry lab and familiar with laboratory techniques to perform many of these tests. The main museum reference for these tests is:

Odegaard, Nancy, Scott Carroll, and Werner S. Zimmt. (2005) Material Characeterization Tests for Objects of Art and Archaeology.  Second Edition. Archetype Publications Limited. London.

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