Copper alloy objects with zinc sulfate efflorescence

I am a student at the Conservation and Restoration program of the
University of Amsterdam, with metals as my specialization.
Currently I am working on my master thesis, the subject being the
growth of white crystals on an outdoor sculpture.  The objective of
my thesis is to investigate the causes and growth mechanisms of the
crystals.

This sculpture is made of a copper-zinc alloy with small amounts of
tin, lead, iron and some trace elements such as manganese.  The
crystals that have grown, and are still growing, have different
morphologies, ranging from thin, fibrous crystals to aggregates of
globular crystals.  Through X-ray diffraction and energy dispersive
X-ray spectroscopy analyses that have been performed on samples it
could be concluded that the fibrous crystals consist of hydrated
zinc sulfate and the globular crystals consist mostly of calcium
sulfate with some calcium carbonate.

Some images of the crystals can be found at

    <URL:https://www.flickr.com/photos/143605564_at_N02/>

I am interested in knowing if these types of crystals are a common
problem.  I would very much like to know what the alloy of the
object is and in what conditions the object was when the crystals
started growing.  Maybe there is an image of the crystals and/or
object is available.  Also I am interested in knowing what kind of
(conservation) treatment the object has received and if that
prevented the crystals from coming back.

Marianne Nuij


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                  Conservation DistList Instance 30:3
                   Distributed: Friday, June 3, 2016
                        Message Id: cdl-30-3-014
                                  ***