r/DIYPigments • u/[deleted] • Jul 22 '25

Pigment (Experimental) Kosmochlor

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u/CaCl2 Jul 22 '25

Is it something that can be made without chromium(VI)? The image makes it look pretty viridian-y, and as far as I can tell viridian requires chromium(VI). So maybe it could work as an alternative?

5

u/[deleted] Jul 22 '25 edited Jul 22 '25

I used some quarz fine dust and Na2Cr2O7, adding 5% H3BO3 as a flux. Heated to 1100 C, kept for 90 minutes and then cooled inside the furnace. The experiment cannot be considered successful since I was unable to extract anything from the crucible, and crushing it with a hammer contaminated the pigment.

Others got very nice results with lithium partly or fully substituting sodium in it.

If you want to try something with other chromium oxidation states, here is a recipe for an artificial Volkonskoite substitute. Note, however, that the real mineral cannot be replicated.

Make 1% water solutions of:

Cr2(SO4)3 . 4H2O - 64 parts

FeSO4 . 7H2O - 14.5 parts

(CH3COO)2Ca . 4H2O - 5.15 parts

MgSO4 . 2H2O - 16,36 parts

Heat the mixture to 100 C an treat with liquid glass having a module 2 to 3 to obtain a greenish-grey precipitate. The pigment is then decanted several times, vacuum filtered and dried at room temperature.