Brian and George, I was totally blown away by your fast, and thourough response. Thank you so much.
I limited my questions to two per visit like I have to at my family physician, but I actually have one more, also about Lead-White.
After repeated levigating, and grinding the Lead-Carbonate flakes, (in a ball mill with ceramic media), I start doing the rinses, usually about ten. Residual Lead-Acetate is found to be present in at least the first four rinses when tested for with Sulfuric Acid.
I precipitate the Lead-Acetate out with Sulfuric Acid, or Sodium Bicarbonate, to end up with Lead-Sulfate and Acetic Acid, or Lead-Carbonate and Sodium Sulfate (environmentally safe concrete sealer).
The Lead-Sulfate is re-combined later with the Lead-Carbonate through a last grinding, followed by distilled water rinses. I read somewhere that this makes a better (oil) paint then if either one was used alone.
I would very much appreciate your opinion on this. BTW I will now also return the pigment from the foam to it`s respective Carbonate.
Thanks, Niq
paint making
Thank you once again George for your answers.
I have used Google to find the excact quote I have in my notes but so far the only thing showing verbatum is from a 1928 publication by Certain-teed paints & varnishes. Not the one I was thinking of but here goes; ” mixtures of Carbonate White Lead and Sulphate White Lead form a combination which is superior to either one used alone.”
This has nothing to do with Artist quality paints but is about coatings.
Arthur H. Church in ” The Chemistry of Paints and Painting” p.114 White lead ” it has been observed that White Lead is less liable to be blackened by sulphuretted hydrogen and by other sulphides when it contains a small quantity of lead sulphate” Not much of a problem anymore I think. Yet another source mentions that it might be a good idea if it didn`t leave the door open to adulteration. One solution for me might be to split my next batch into half and finish one half with the sulfate added back in, the other half straight carbonate and see if I can even notice a difference.
Thank you.
paint making
From; The Chemistry of Paints and Painting, by Arthur H. Church p114
” It has been observed that White Lead is less liable to be blackened by sulphureted hydrogen and by other sulphides when it contains a small quantity of Baryta White or of Lead Sulphate thouroughly incorporated with it by grinding “
Whereas solutions of sulfuric acid and lead(II) acetate react to form solid lead(II) sulfate and a solution of acetic acid, this simply increases the impurities in the product. Where did you read that lead sulfate is beneficial? I have never read this and would be curious to know the reference, otherwise I have never encountered this in literature.
Georg Zerr writes in A Treatise on Colour Manufacture (page 115) about testing for the presence of lead acetate:
“It is very easy to ascertain whether white lead contains lead acetate by pouring a small quantity—about twenty to thirty grms.—into a porcelain basin with water, and heating it carefully over a flame, the whole being kept stirred. The liberated water vapour will have the characteristic smell of acetic acid and redden moistened blue litmus paper, owing to the presence of that acid. The aqueous solution will deposit a white precipitate of lead sulphate on the addition of sulphuric acid.”In the preceeding paragraph he remarks:”White lead that has not been sufficienlty purified from adhering lead acetate has the sometimes troublesome property of making paint dry very quickly. A paint of this kind, containing about 6 to 7 per cent, of linseed oil, will on being kept get hard and lumpy, requiring protracted treatment to make it fit for use again.”
The issue of the alteration of lead white due to the presence of hydrogen sulfide air pollution is less a concern today than it was when industrial countries burned coal. I am not sure if the statement by Church is accurate science; I cannot see how sulfide pigments can prevent this type of issue ocurring in the presence of this type of air pollution. Anyway, I think you may be overreaching by being concerned by this issue.
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