Displaying brass in water

Lynn Campbell <lynn.campbell [at] ccc__govt__nz> writes

>There has been a proposal to display a brass art work in a pool of
>water at our gallery.  ...
>... any advice on this topic for
>my report on the proposal would be most useful. Can anyone help?

(1) It largely depends on the quality of the water. If the water is
low in dissolved solids and neutral in pH there should be little
effect over a short period of time (years rather than decades) on
most brass alloys. Long term effects could include general
corrosion, dealloying (selective dissolution of copper or zinc for
example), deposition of scale (e.g., calcium carbonate scale from
hard water), and etching (to reveal crystalline grain structure of
the metal). (2)  There is more than one brass alloy, any testing or
evaluation should consider this, and (3) more importantly is the
brass in question physically in contact with another metal (such as
a solder or with steel screws). This could promote galvanic
corrosion, perhaps on the solder or screws if present. (4) The
corrosivity of the water on the object in question is easily
determined by electrochemical tests available through corrosion
testing labs. (5) There are corrosion inhibitors that can
essentially block corrosion of the brass when present in the water
at approximately 100 parts per million.

Some of these inhibitors will protect several metals at once (even
against galvanic corrosion) but their concentrations must be
maintained. Their performance is easily measured for any particular
case. Local (industrial) water treatment companies and corrosion
testing/consulting services can most likely advise you (with hard
data to support their advice) on exactly what will happen in your
specific case and how to best address protection of the object from
corrosion. I hope this helps,

Dr. Michael Whitbeck


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                  Conservation DistList Instance 16:76
                   Distributed: Friday, May 30, 2003
                       Message Id: cdl-16-76-005
                                  ***