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Is it possible to selectively re-patinate worn away areas of black patination on brass

February 21, 2009

I am renovating a 1920s/30s telescope made with chemically blacked not black painted brass. The patination has been worn away on a small area of the sliding sunshade. I have fixed the cause of this and I would like to re-patinate this area, but is this going to be possible?

The patination is not a true black but is a medium grey 'graphite' colour with a hint of blue. The solder lines are a much lighter tone showing that the chemicals used did not take well on solder.

I had read that copper carbonate in ammonia [on eBay or Amazon] gives a blue black on brass and does not take on solder so I tried various strengths of this solution. It worked well on a brass screw head but not on the telescope. I tried on a hidden area where the patina was rubbed away. Even after cleaning the area by scrubbing with detergent and wiping with strong ammonia the mix had no effect. I tried abrading a tiny area down to the pure brass but even here the result was poor with the borders of the area not 'taking' and the centre uneven.

I wondered if ammonia vapour and a dampening of the brass with vinegar [in bulk on eBay or Amazon] might be worth a try or one of the manufactured products which uses selenium to lay down a copper coat to improve the 'taking' of the blacking. Or is this an impossible project - I am not going to risk an attempt at stripping and re-patinating the whole component. I would welcome any expert advice.

John Francis
hobbyist - Lincoln, Lincolnshire, England

You can download(free)old English book on metal colouring by Arthur Hiorns (www.archive.org).There are many black patinas for brass-you can cover good parts with some protective coating and then you can try to colour only bare metal parts(oxide and grease free)-it is very complicated if not impossible to match old colour without exact identification of used process(even then it can be impossible).It is much easier to remove old patina(but absolutely wrong fom metal conservators stand point) and then You can try to renew old finish.Hope it helps and good luck.

Goran Budija
- Zagreb,Croatia
February 26, 2009