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tango

Grinding natural pigments

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Hi
Two weeks ago was the first time I grind natural pigments. Previously I mixed some oil tubes colours with some synthetic powder pigments using a muller over a glass.
This last time I grinded cochineal powder from Kremer and a lake, made by me, from a tree called "Quebracho" (Schinopsis balansae), very rich in tanins.
I never noticed any change in color grinding sintetic pigments like Quinquasia Gold or others but with this two natural ones I saw a change in color as I insisted grinding.
May be that natural powder brake into pieces and free some hue?
I grind with some drops of oil, a little of turpentine and finally a little of oil varnish. Then mix all with varnish.
Thanks in advance for opinions
Tango

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Much of this has been noted in other threads.
 

Cochineal and madder are very sensitive to pH. The molecular charges in the medium (measured by pH) twist and bend natural colorant molecules which changes their color. Modern organic colorants usually have strong structures that are not altered by the charges in the medium. Chemists spend a lot of time and money perfecting these resilient pigments. 
 

BTW, linseed oil can sometimes protect organic pigments if the oil completely surrounds the molecule. Moreover, the complete immersion in oil reduces light reflections (scattering) that obscure the pigment color. This is why good mulling is important. 

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22 hours ago, tango said:

Hi
Two weeks ago was the first time I grind natural pigments. Previously I mixed some oil tubes colours with some synthetic powder pigments using a muller over a glass.
This last time I grinded cochineal powder from Kremer and a lake, made by me, from a tree called "Quebracho" (Schinopsis balansae), very rich in tanins.
I never noticed any change in color grinding sintetic pigments like Quinquasia Gold or others but with this two natural ones I saw a change in color as I insisted grinding.
May be that natural powder brake into pieces and free some hue?
I grind with some drops of oil, a little of turpentine and finally a little of oil varnish. Then mix all with varnish.
Thanks in advance for opinions
Tango

Mineral pigments and pigments captured in a good mineral lake tend to be stable. But organics not protected in a lake or otherwise can be sensitive in many ways.

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Hi
I am understanding a little joining replies.

As I insisted grinding the color was getting some dark. I guess it was due to the "quebracho lake" (tanins) not the cochineal because I tried a couple of test and cochineal didn´t change during the grind with muller. I will pay attention to the medium used in the grinding process (Turpentine, oil or varnish)
Thanks all for your help
Tango

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The tannin from quebracho is not a lake, namely a pigment particle. It is a dye that becomes attached to cellulose with a mordant. Grinding quebracho will achieve nothing. I think quebracho is the loveliest tannin. I recall @Johnmasters calling attention to this several years ago in a thread. Cochineal, however, is a made into a lake. Good mulling is needed to totally wet the particles with oil.

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On 7/28/2020 at 12:53 PM, Michael_Molnar said:

The tannin from quebracho is not a lake, namely a pigment particle. It is a dye that becomes attached to cellulose with a mordant. Grinding quebracho will achieve nothing. I think quebracho is the loveliest tannin. I recall @Johnmasters calling attention to this several years ago in a thread. Cochineal, however, is a made into a lake. Good mulling is needed to totally wet the particles with oil.

Hi Michael
I made a lake from the dust of sanding of quebracho.
I went to a carpentry and bought that :) 

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hi david
I don´t remember well but it was some like this
I made a Lake pigment mixing quebracho sanding dust in a jar with "carbonato de calcio" wait for the time needed then added alum . Waited for decant and siphon clear water. I repeted that several times. Filtered that  and let dry  and so obtained the lake pigment.
I made two. One of pernambuco and one of quebracho.

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