It is the use of old recipes like this and their widespread publication that has helped my hair turn grey over the years!

What may be fine for copper cookware which only has an intended life of a dozen years or so is not a suitable cleaning technique for historic or artistic metals.

This recipe contains vinegar (acetic acid)) mixed with salt (sodium chloride).  These corrosive chemicals will strip away copper ions leaving fresh metal exposed to the surface.  What is "clean" is actually a metal surface that has been stripped away.  What is even worse is that residues of these chemicals will remain within the microscopic pores and seams in the metal leaving serious damage to occur months and years down the road.  Think about the corrosion of metals in areas by the seashore - would you deliberately expose an art or historic object to these conditions to "clean" them?  (by the way - chloride salts from fingerprints leave their indelible marks too!)

Always be immediately suspicious of any metal cleaner or polish that works instantly!  That is a clue that it is either too abrasive or corrosive.  Modern polishes and cleaners are often formulated this way in order to appease our need for instant results.  Most modern brass polishes, Brasso as an example, contains ammonia and ammoniated chemicals and pretty harsh abrasives.  Ammonia is a powerful degreaser but it can cause significant damage to brass alloys by the mechanism of stress corrosion cracking - the abrasives drive the chemicals in intimate contact with fresh metal and then the residues remain as loccii for future corrosion.  This damage takes many years to become visible to the human eye and by then it is often too late.

Now, when faced with polishing the brass on a large industrial object - such as a locomotive you have an economy of scale to consider. Also, the environment that surrounds the object / artwork is an important consideration in formulating a cleaning and preservation plan.  There are safe alternatives to the commercial products.  Your best bet is to call the American Institute for Conservation and to get a free referral for a metals/objects conservator in your region  (202-452-9545) or send them an e-mail at:  [log in to unmask] .  Most conservators will come out, look at your problem, and give you advice on cleaning for a reasonable fee.

As I have said numerous times on this list, conservators do want to help to give you advice that you can use.  We hate having to tell people "no" all of the time.  That usually occurs because people often act before asking.

I have written a series of informational pamphlets on the care of various metals.  I would be happy to send those out free to whomever requests them.  Just contact me off the list.

Cheers!
Dave

David Harvey
Associate Conservator,
Metals & Arms
The Colonial Williamsburg Foundation
P.O. Box 1776
Williamsburg, Virginia  23185-1776  USA
Voice:  757-220-7039
E-mail:  [log in to unmask]

-----Original Message-----
From:   Douglas W. St.Clair [SMTP:[log in to unmask]]
Sent:   Tuesday, June 30, 1998 9:30 PM
To:     [log in to unmask]
Subject:        Re: Brass and copper

John,

I used to work in a kitchen as a pot washer. The chef made a mixture of
salt, vinegar, and flour to clean the copper pots. The recipe went as
follows: Take a bottle of vinegar, dissolve as much salt in it as you can
(leave a teaspoon undissolved at the bottom is fine), at flour to thicken
it make a paste to taste <g>. Just spread the stuff on copper and you can
see it brighten immediately. I used to wait about five minutes then wash it
off. The color of copper with this stuff is a little redder than the
commercial products but there are no abrasives,  its fast, and cheap. You
could try it on brass I never had the need to see what it would do.


>
>I am looking for good guidance in preserving brass and copper on 1800s
>steam locomotives.  I am worried because the brass is in excellent
>condition and I don't want to damage it.  Current procedure uses an
>industrial cleaner, but I wonder if it is stripping the brass away.
>
>Thank you
>John Hunter
>Curator
>Kennesaw Civil War Museum
>"Home of the General"
>
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Douglas W. St.Clair
Tir Na Nog
400 Burton Highway
Wilton. NH 03086-5022
PH: 603-654-9321
FAX: 603-654-5440
EMAIL: [log in to unmask]
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