Brass

Michiel Langeveld <info [at] metaalrestaurator__nl> writes

>During washing of brass objects in water, the brass stains from gold
>to brown. Can anyone advise me on the use of inhibitors or other
>methods to avoid this staining?

I have found that brass I have cleaned in a similar fashion also
tarnished quite quickly.  I think in my case the tarnish was caused
by contact between the brass artifact and the stainless steel basin
in the ultrasonic tank, which set up an electrolytic cell.  If you
can use a barrier between the floor of the tank and your object, you
might have better luck.  You might also consider eliminating the
ultrasonic step, unless you are trying to remove particulates, which
it is best suited for.  EDTA should be easily removed with a quick
rinse with water and a surfactant.  Also, I think you might be
rinsing the brass in water for too long.  Unless the brass is really
porous, it should not be necessary to rinse it for more than 30-60
seconds.  I try to keep the brass in a wet state as little as
possible, and I try to dry it as thoroughly as possible as soon as
possible, so as to deter corrosion.  It seems that since brass is an
alloy, there may be some areas of the alloy that differ slightly in
their metallic composition and crystalline structure.  This makes
some areas more prone to rapid corrosion than others, and this may
explain what you are experiencing.  What I try to do is clean the
brass with EDTA, quickly rinse with a surfactant and water, then dry
it with a clean cotton cloth, degrease with acetone, dry in an oven
at about 60-70 C for about 5-10 minutes, and then apply a coating of
either Acryloid B-48 or cellulose nitrate lacquer.  I find having
the artifact slightly warm also reduces the likelihood of the white
blooms you can sometimes get in warm humid weather.  I hope this is
helpful, take care,

Thomas J. Braun
Daniels Object Conservation Laboratory
Minnesota Historical Society


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                  Conservation DistList Instance 18:9
                  Distributed: Thursday, July 22, 2004
                        Message Id: cdl-18-9-006
                                  ***