SV: Cleaning Metal Threads

[Bodil Taarnskov <Bodil.Taarnskov@xxxxxxxxx>]

Dear Rebecca,

Since I haven´t seen the object with the green and black corrosion, I don´t know how important it is to remove it. Metal threads of  gilt or silvered copper will often turn into an unpleasant reddish color, if the corrosion is removed, because the gilding and silvering isn´t complete.

I therefore recommend, that you only clean of the loose dirt and corrosion products with a mixture, which is able to dissolve some copper- and silver oxide and chloride compounds - but not all. It may brighten the object but not remove the green corrosion.

The mixture consists of: approx. 50% demineralized water, 45% ethanol and  1-5% ammoniumhydroxide. 

The ammonia rises the pH of the solution. Therfore it sometimes changes the color of the wool, if the concentration exceeds 5%.

Because of the composite object with stiffening material etc., the cleaning must be done with a cotton wool swab or a very small brush, in order to keep the materials beneath the metal threads dry. All the components in the solution will evaporate and leave nothing behind.  

I have worked with metal threads in epaulets, fringes, tresses and bands during some years. In most cases you can only remove the loose dirt, because metal salts are not soluble in water, detergents or solvents. You need chemicals or electrochemical methods.
Chemicals, witch are capable to dissolve corrosion products are alkaline or acidic (and therefore not suitable on textiles) and the electrochemical method both require water for rinsing after treatment.

The other problem with most textiles decorated with metal threads is, that it is often combined with materials, which you cannot dip into a liquid - as in the case of your epaulets, witch contain stiffening like starch or glue.

I have worked a lot with an electrolytic method on bands and fringes made of gilt silver around a silk core, witch could be removed from the object and dipped into an electrolytic bath. The electrolytic process was measured potentiostaticly keeping exact parameters, and carried out in two steps: First the silver corrosion was reduced into metallic silver, witch resulted in a dull grayish surface. The second step was a very short oxidation that removed the silver and unveiled the golden surface. The electrolyte was appr. pH 5. 
I don´t think this method is suitable on metal threads with copper under silver or gold, because the silvering and gilding is so thin, that the copper will dominate the appearance. Besides, the gilding and silvering may fall of during the cleaning.

The electrochemical method described by Timar-Balazsy and Eastop ( used by Columbus and Miller, i suppose) has the disadvantage, that you probably will get this grey surface of porous metallic silver and a reddish layer of reduced copper, witch you cannot remove with that method.

Good luck with the work.

Bodil Taarnskov
Conservator
The National Museum of Denmark
Conservation Department
DK-2800 Kgs. Lyngby
tel. +45 3347 3502

        

-----Oprindelig meddelelse-----
Fra: Textile Conservators [mailto:TEXCONS@xxxxxxxxxxxxxxxxxx]På; vegne af
Rebecca Tinkham
Sendt: 28. marts 2006 18:27
Til: TEXCONS@xxxxxxxxxxxxxxxxxx
Emne: Cleaning Metal Threads


Hello all,

I am working on an early twentieth century military uniform with tarnished
metal wires on the epaulets.  The epaulets, which can be removed from the
rest of the uniform for cleaning, have silver and gold plated copper alloy
(possibly brass) threads couched down with a waxed cotton thread to cotton
velvet, wool, and a stiffening fabric.  The silver metal is black and the
other metals have a greenish corrosion product on the surface.  I would like
to brighten the metals and remove some of the loose surface corrosion
products.  The threads and fabrics are all in good condition.

After reading through various approaches for cleaning metal threads, the use
of a water, perc., and non-ionic emulsion with a soft brush described by
Timar-Balazsy and Eastop or an electrochemical method seem to be gentle to
both the metal and fabric elements.

I would like to know what experience other conservators have had using these
approaches.  Were you happy with the cleaning achieved?  Did you see any
kind of redeposition back onto the metal or fabric?  What, if any, long-term
affects have you seen to the metal or fabric elements?

Thank You,

Rebecca Tinkham
Conservation Department
Museum Services Division/DCA
P.O. Box 2087
Santa Fe, NM
87504-2087
rebecca.tinkham@xxxxxxxxxxx