> Also it was said that several "glazing" coats of yellow as the
last coats would work. In truth I don't understand this yet. It would seem
that if the colour is not transparent then several thin coats to build up
density would be as opaque as fewer coats. Also as I normally do between 4
and 8 coats of yellow already,<
The thing is bernie that glazing is a way of making a an opaque colour,
transparent
and works on the principal of building up a number of coats containing
little or no colour as these coats are piled up one on top of the other to
reach the final colour
value, this layer has become very thick and therefore allows light from the
underneath colour layers to pass around the pigment particles and shine
through.This method has been used traditionally by painters to give those
transparent flesh tones so typical of historical painting, even modern
painters use this technique Salvador Dali is said to have used over forty
glazes per colour.
As you say that you are already using up to eight coats per layer you are
in fact glazing and not aware of it.
>yellow is most sensitive to what I call tanning. That is, the tendency
of the gum to turn brown when exposed. <
I don't think that the yellow is actually discoloured more by dichromate
stain than the other hues it just appears to be so due to the fact that the
yellow has the highest tonal value and the eye will be more sensitive to
it.
> My tests indicate that it takes an extremely long wash time (over 12 hours) to
get rid of this staining. <
I have just completed a series of tests on the removal of dichromate
stain, which I hope to share with the list during the next few days when I
get them wri tten up.However I can say with certainty that the best method
is a 1% solution of sulphuric acid,and the least effective the long wash,
however at short exposures times it will work, but still not as effectively
as the dilute sulphuric acid, which completely removes the stain for all
practical purposes.Normally this bath will clear the stain in 2 to 5 mins.
>Judy once said "Everything affects contrast" I would like to expand on that
corollary to "Everything affects everything".<
Very good I like it, and will probably use it on my students
pete.