Thursday, February 2, 2017

Explaining Differences in Paint Colors with the Same Pigment Number

Linda Working on a Color Chart
Thanks again to all who attended our Jan. 30 meeting!

A question came up about paints with the same pigment number that are different colors. Linda Koffenberger, (who teaches art at NCBG and has a professional background in paint color mixing), answered our question here:

"The first example is Ultramarine Blue, which comes either with a red bias or a green bias.  Both are coded as PB29.  The reddish-toned Ultramarine is usually sold as French Ultramarine and the cooler, greenish-toned one is sold just as Ultramarine Blue.  Originally Ultramarine was a mined pigment made from Lapis Lazuli and was the most expensive pigment there was.  Then in the 1800's, a way to manufacture it was invented.  The process uses silica (or sand) and "Ultramarine poor in silica" has the greenish-tone and the "Ultramarine rich in silica" as the red tinge.

The second example is Yellow Oxide, a naturally occurring mineral.  Its chemical name is iron(III) oxide-hydroxide.  It is sold under the name Yellow Oxide, however, and the code on the tube is PY42.  The thing is this mineral can be any where from yellow to dark-brown and even black.  So the pigment manufacture tries to blend batches to make the color uniform from one tube to the next.  But another manufacture may have a slight different blend so the color varies from manufacture to manufacture."