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Subject: Brass coatings

Brass coatings

From: Jane Ketcham <ketchamj>
Date: Saturday, December 24, 1994
In response to Alan Hawks query concerning lacquers:

Dragon's Blood is listed in the current Merck Index as

   "A resinous secretion found on the fruits of Daemonorops propinquus
    Becc., D. draco Blume, and probably other species of Daemonorops,
    Palmae (Rattan palms). Habitat: Sumatra, Borneo, India....Red
    sticks, pieces, or cakes; makes a bright-crimson powder; odorless
    and almost tasteless. Used for coloring lacquers and varnishes;
    occasionally for coloring plasters; in photoengraving on zinc to
    protect metal parts against etching."

I think it is likely that the term "Red Sanders" refers to sandarac,
rather than sandalwood. Sandarac was a common ingredient in lacquers,
and is still used for some. The Kirk-Othmer Encyclopedia of Chemical
Technology describes sandarac as the resin of Callitris quadrivalvis, a
coniferous tree native to the Atlas mountain region of North Africa. "A
number of the Australian Callitris species yield a pine gum or
Australian sandarac. The African variety, exported chiefly from Mogador,
Morocco, is in a form of yellowish lumps, dusty on the outside and
readily pulverized." Soluble in alcohol, it is used as a primer for
metals, in lacquers, varnishes, and as incense. As both of these
materials are described in current references, I would assume that they
are still available for some industrial uses. A good art supplier might
be able to locate them.

As to future care of historic scientific instruments, I would urge the
collector to avoid removing original lacquers in the future. Although
the instruments may not appear pristine, it would be better to limit
activities to simple cleaning, avoid removing original materials, and
eliminate the difficulties of trying to "restore" the finish. If active
corrosion is a problem, it would be best to have a conservator look at
the affected pieces to suggest appropriate treatments.

Jane Ketcham
Conservator in Private Practice
Beloit, WI

                  Conservation DistList Instance 8:49
                Distributed: Tuesday, December 27, 1994
                        Message Id: cdl-8-49-006
Received on Saturday, 24 December, 1994

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