Resources for Paint Pigment Microscopists
||Joe G. Barabe, McCrone Associates, Westmont, IL
For a microscopist, some of the most interesting subjects of
inquiry are paint pigments. Their identification is often a crucial factor in
establishing when a painting was made, which can shed light on its attribution
or authenticity, or the nature of an architectural coating, which may affect
treatment and restoration strategies. A third area, automobile paints, is a
specialized field of forensic science and will not be discussed in this column
at this time.
In order to successfully identify pigments from a painting,
object or architectural site, the microscopist needs reference samples that
adequately cover the range of possibilities, reference texts, the proper
instrumentation, and, if possible, an experienced mentor. Here is a list of a
few resources useful to learning and practicing pigment microscopy:
Reference Samples: Pigments
Comparison of the questioned material with known reference
samples is absolutely critical, as microscopy is a highly visual analytical
technique. Some of my favorites are the following:
Kremer Pigments ( www.kremer-pigmente.com
) is one of my favorite sources. They sell dry pigments without
binding media (such as gum for watercolor, oil, casein, vinyl, acrylic,
and so forth), which make them ideal for reference material. They sell
them in bulk, which is good if you are sharing the material or need extra
for other instrumental references. They also sell paint swatch samplers
of their pigments, which is the easiest way to get a wide variety of pigments.
A full set costs about US$130, and you can purchase individual sets of
selected colors for about US$10 each. The most important set is the chart
of Historical Colors, 60 samples for US$18 (Figure 1). Wonderful! This
is the best way to acquire a comprehensive collection for the best possible
price. They also sell a full collection of bulk samples of the important
historical pigments in an attractive case – very nice!
click image to enlarge (182K)
Kremer Color Chart 001: Historical Colors
Making reference microscope slides from the sample
swatches is simple:
- Scratch the surface of the swatch with a needle, covering
a moderately broad area, to loosen a good number of particles.
- Prepare a microscope slide by putting a drop of mounting
medium (I use Cargille’s Meltmount™, refractive index 1.662) in the middle
of a standard 1” x 3” (25 mm x 75 mm) microscope slide.
- Warm the slide on a hotplate to spread and flatten the
- Allow to cool.
- Collect the loosened pigment particles by pressing the
flattened drop repeatedly over scratched areas.
- Coverslip the preparation and place onto the hotplate to
melt the mounting medium.
- Remove from the hotplate and press the coverslip to
disperse the pigments and mounting medium.
- Label the slide. Store the slides flat. Done!
The resultant slides are of very good quality, with the
pigments (usually) very well dispersed. Figure 2, cobalt violet brilliant
(PV49), taken with plane polarized light at 400X magnification in Meltmount ™
(1.662) is a typical preparation.
click image to enlarge (179K)
of Cobalt Violet Brilliant (PV49), Kremer number 45820, from the
Kremer Chart006 Blue Pigments. Plane polarized light at 400X,
Meltmount™, refractive index 1.662
click image to enlarge (167K)
McCrone Paint Pigment Reference Set from McCrone Microscopes and
Of course, the easiest way to get a high quality
set of ready-made pigment reference slides is to purchase a Pigment Reference
Set of microscope slides from McCrone Microscopes & Accessories (www.mccrone.com),
which includes 50 of the most important pigments (Figure 3). McCrone Microscopes
& Accessories is also an excellent source for all kinds of microscope
supplies, such as microscope slides and coverslips, refractive index liquids,
mounting media, hotplates, microscope labels and the like. Other scientific
supply venders may also have these materials available.