Article Reconstructing Van Gogh’s palette to determine the optical c...

Muriel Geldof, Art Néss Proano Gaibor, Frank Ligterink, E. Hendriks,

E. J. J. Kirchner,

Thank you very much for having published your article online. I have read it with the greatest interest.

You wrote that " the amounts of oil used in the reconstruction

paints largely exceed the amounts expected based on

these values in literature. This might partly be explained

by the fact that we were aiming at relative fluid paints.

Yet other factors might also play a role: oil absorption

values largely depend on pigment particle characteristics,

as size and shape, as well as on the paint manufacturing

process; paints produced from grinding by hand with a

muller may contain considerably more oil than modern

machine-ground paints. Moreover, eosin and

chrome yellow tube paints that were presumably used by

Van Gogh appeared to contain an excess of oil as well."

I can give you another information about these Oil Absorption figures. The values published in literature are not actual amounts needed to create workable paints. They are copied from industrial pigments data obtained by "Gardner-Coleman" tests. In these pigment testings, oil is added, drop by drop, the mix being thoroughly rubbed with the spatula between additions until a very stiff putty-like is obtained. In most laboratories, operators make this paste compact and stiff enough not to adhere to the slab and spatula. It looks like heavy old style children's modeling paste, not paint.

When dispersing pigments in oil to make artists'paints, even if we want these paints to be stiff, we must indeed add more oil. As examples, I can give you a few OA measured by myself (hand ground paints, on a glass slab with granite, marble or glass mullers).

Ultramarine : 36-40g oil / 100g PB29.

Blanc fixe : 21g oil / 100g PW21

Chalk : 19g oil / 100g PW18

I hope it will help.

Best regards,

Thierry Moutard-Martin