A question about Cobalt Green.

[Carcharhinus]

I'm wondering if this would be better served in a big thread about differences in pigment hues, so we can have a big discussion, but I have a question or two about Cobalt Green.

I'm looking at buying this colour, in oils, by Williamsburg:



It's PG50 Cobalt Titanate Green. Williamsburg calls it Cobalt Teal.

This is how the same pigment looks from some of the other manufacturers who carry it. Here we have Blockx Cobalt Green Light, Old Holland Cobalt Green and W&N Cobalt Turquoise Light.





They all look quite different, as you can see.

My question is why? What happens to the Cobalt Titanate Green that it can take on so many different hues?

Second, if I were to buy some of this pigment dry in order to save money, is there anything I can do to the pigment to change its colour? For example if I got a Cobalt Titanate Green powder that matched the Old Holland, is there a process that I could go through at home with the standard safety equipment (Gas/dust mask, gloves etc) that would change it to look like the Williamsburg or vice versa. I know this is a long shot since I don't have a laboratory, but maybe there's a trick.

I understand some basics about changes in hue with the same pigment. I know that PR101 depends on such factors as pigment hydration to give it its different shades, and that PBr7 actually encapsulates a number of different earths, both synthetic and natural, but I have no idea about the Cobalts.

[Gigalot]

I have 3 different PG19 Cobalt greens and one PG26 Cobalt chromite blue-green.
Manufacturing process to make Cоbalt green PG19 contains zinc oxide impregnated with a solution of cobalt nitrate and heating the mixture at high temperature. Cobalt green light version needs less cobalt concentration and and short heating time. Cobalt green deep needs more cobalt nitrate and longer heating time.
If you need to prepare Cobalt Turquoise light, you must heat Zinc oxide + Cobalt nitrate and alum solution. Alum additive needs to make a cool versions of cobalt green light.

[yellow_oxide]

From Handprint.com (link directly to PG50)

The same color index name refers to a range of cobalt spinel pigments of different hues, caused by differences in the proportion of aluminum, nickel or zinc in the crystal. (A "spinel" is a crystal framework formed of magnesium aluminum oxide; other atoms chemically fit into this lattice to produce different colored compounds.)

It goes on to explain that there's three varieties- teal, bluish green, and yellowish green.

In oil paint I have both the bluish and yellowish green varieties from Blue Ridge, called cobalt green deep and light. The deep is nearly identical to viridian to me, but a little lower chroma, and the light is an attractive yellow green that's yellower and brighter than the swatches you have. I like both of them.

If you want to save money, I'd suggest Cobalt Turquoise (PB36, which comes in two varieties, this being the greener one while some cerulean blues are made from the bluer one) from Blue Ridge. I found their cobalts to all be excellent and cheaper, sometimes far cheaper, than the brands you mentioned.

[karenlee]

Very interesting. Thank you all.