In certain years, the Royal Mint blackened farthings (1/4 pence) so they would not be confused with half sovereigns. See the pic. How did they do it? Cal
Freeman states they were oxidised using acid fumes (p.118), but doesn't expand on the precise acid used. Peck is less explicit, merely stating they were issued with a blackened finish at the head of each relevant section.
Interesting. Mintages were in the millions, so I wonder what kind of machinery was used to expose that many coins (or was it the planchets?) to fumes and do it pretty evenly. Cal
That would do it alright. But so would ordinary toning over a long period of time. Acid fumes in the air in a closed room would do it pretty quickly, a day or two I would think. The coins would have to be laid out flat on a surface, then flipped over to do the other side. Bottom line it's nothing more than deliberate and greatly accelerated toning.
