In my research of historic pigments thus far, I have come to this conclusion. The main difference between the modern day pigments and those of the 17th century is particle size. Modern paint makers use technology which enables them to grind paints to a uniform smooth consistency. The grinding techniques or the synthetic process by which paints are made produces particles of similar shape. The size of these particles is approximately 5 to 10 microns(very small).
Contrarily, historic colors were made by hand by crushing stones such as lapis. The end result was a pigment with many varieties of shapes and sizes: perhaps up to 120 microns (much larger).
As light passes through layers of paint, it is bent by the particles. When paint has tiny particles (5 microns) like modern paints , there is not much refracting occurring. But when light passes through paint with larger size particles like the masters used, much light bouncing happens. This clearly illustrates the advantages of using historic pigments and grinding techniques.
Back to the grinding wheel next time!
HI Margret,
Do you by any chance use Kremer Pigments?
I work there part-time and this is sooo familiar to me and not at all to almost all other artists. I like the way you explain things!
Carolg