Talk:Purpurin (glass)

Metallic copper or Copper(I) oxide?

The article claims that the color of purpurin glass is due to metallic copper particles. However the newsletter in the External Links section says that it is due to precipitation of copper(I) oxide. This claim matches my recollection of a similar explanation given in pottery boooks about the blood-red copper glazes.

Also the loss of color in smelting may not be due to smelting per se but to oxidation of copper(I) to copper(II). Presumably if the glass is melted in a reducing atmosphere it will preerve its red color.

All the best, --Jorge Stolfi (talk) 19:04, 21 February 2010 (UTC)[reply]

You might very well be correct, although there might be a difference between transparent and opaque red glasses. Glass chemistry is not my specialty. I wrote this more from the historical perspective, and original German investigators (as well as the German encyclopedias from the late 19th century) seem to have been of the opinion that with the opaque "Hämatinon" reduction proceeded all the way to metallic copper. Even later literature seems to take an ambiguous position. Here is a reference from India which I googled up but did not cite (because its full biography could not be found on the databases I have access to): http://www.new.dli.ernet.in/rawdataupload/upload/insa/INSA_1/20005b64_272.pdf - This is surely much more recent (though the latest reference it cites is from 1968). On p. 273, par. 3, line 4 it says: "red - Cu2O, Cu (red hematinum)." Perhaps Wiki Group Glass has authoritative data available? - Greetings, Glst2 (talk) 08:57, 22 February 2010 (UTC)[reply]