Question asked 2018-01-11 19:49:01 ...
Most recent comment 2018-01-23 01:13:28
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.
Answers and Comments
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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