Letter 15023

Colour Change [England] 

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I want to change some brass candlestick holders from brass to black without ruining them.

Gill Manning
- Hertfordshire, England

There are two basic options. Both involve making sure the brass is very clean before you start or you will have problems with adhesion and good film thickness. I suggest you give the brass a very good clean in both acid and alkaline cleaners; the exact process will depend on what you have available. You can then paint the brass with a suitable paint; probably acrylic is the best option, although if you have access to electrophoretic paint, this is better as it will get into all nooks and crannies and will give a more consistent coating.

Secondly you can dip the brass into a sulfur solution. This is usually made by dissolving flowers of sulfur in a solution of sodium sulfide. The solution will go a sort of yellow colour and will stink, but it is very good at blackening metals. However, its success may be dependent on the type of brass you are using as different brasses have different amounts of zinc in them.

To get best consistency, try carefully etching out the brass from the surface, but be careful, as removing too much zinc will result in "dezincification" which will leave a copper sponge with no structural strength.

Trevor Crichton R&D practical scientist - UK

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