pigmented colorants: dependence on media and time - Cornell ...

5.1.5 Painting
After the layers of gesso had thoroughly dried, the support was ready to be painted.
Many pigment masstones are dark, making it difficult to determine the character-
istic absorption bands. As a result, a tint of each pigment was also made with
titanium dioxide white. We studied 21 pigment mixtures: 11 pure pigments and
10 tints. The measured ratios in tints had to be very precise to ensure reliability
of the data. Tints were made with 50% colored pigment and 50% Titanium Diox-
ide. We combined each pigment mixture with the eight different binding media.
For every pigment-binder mixture, we painted two samples to make sure that we
had a sample of sufficient quality. In total there were 21 x 8 x 2 = 336 painted
samples. The author notes that this does not include the many samples that were
not of adequate quality due to pigment-binder inconsistencies (cracking, clumping,
agglomeration, flocculation, inadequate dispersion, etc.).
One binding media was created and measured at a time (for all pigment mix-
tures). Prior to painting a selection of samples, a specific binding media was made
fresh. Some binding media lose adhesive strength if they are stored and reused at
a later time. A measured ratio amount of binding media to pigment was combined
in a plastic cup. 1 Painstaking care must be taken to prevent any impurities from
entering a paint mixture. Contamination can occur at many stages in the painting
process.
Kubelka and Munk found in experimentation [KM31] that the steel spatula
used to disperse the pigment in the binder left minimal traces of iron in the paint
due to the hardness of the pigment. In the particular case, the white paint had
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1Some pigments are toxic and care should be used in handling the dry pigment
powder to avoid inhaling the dust.