Acetic ageing
I write regarding the letter by Mr Creed, ‘Ageing brass’ in Clocks December 2003.
Being a retired university lecturer in organic chemistry I am not at all surprised that your carefully polished brass is adversely affected by the fumes given off when the mastic hardens. These fumes usually consist of acetic acid which is strongly corrosive, resulting in the brass turning first brown, then green. There are some silicones that give off amines which smell like ammonia. These amines are also corrosive and, worse still, they can give rise to stress corrosion cracking.
One should note that although the majority of the fumes are given off at the beginning of the hardening process and the development of a skin on the mastic slows down the secretion, the fumes are still there and will continue to be given off for a very long time - months or even years!
Provided the glass panels are set in wooden frames and not in contact with brass I would suggest the use of old fashoned glaziers linseed oil-based putty as being safer.
Goran Zdansky, Sweden
|
