Reproducing niello

Renita Ryan <ryan.renita [at] saugov__sa__gov__au> writes

>Does anyone have experience in reproducing niello on a silver item
>that has been stripped back to silver metal?

While refining our Metals Conservation curriculum, I was required to
also conduct trials in the reproduction of niello, which in this
case was encountered in the form of decorative, incised detailing on
an attractive, metal cigarette case in need of conservation.

First, we had attempted to produce niello by a traditional method,
which called for the following ingredients: Silver (6g), Copper
(2g), Lead (2g) and as much pure sulphur as needed for saturation.
We had proceeded as follows:

    1.  Melt the metals in a borax lined graphite crucible, stirring
        with a carbon rod. We used a torch flame.

    2.  Add the sulphur until the mixture is saturated. (Beware the
    acrid fumes!)

    3.  Pour into an ingot mould, or similar, to produce a
        convenient, cigar-like shape.

    4.  If the resulting ingot is not a smooth, shiny black,
        re-melt, add more sulphur and pour once more.

The niello produced in our case by this method was less than
satisfactory. Although the outer surface was a promising, shiny
black, the inside was somewhat porous and almost pumice-like. We
suspect that the sulphur used may have been of an impure grade.
Perhaps someone else will have success with it and give a better
report? This method does, however, produce spectacular amounts of
foul-smelling fumes and smoke, and proper ventilation, eye
protection and breathing masks are therefore essential!

The alternative, and ultimately more successful option, was to
produce artificial niello. This was accomplished by employing a
water-white (clear) epoxy--Araldite 20/20 in this case--which was
prepared in a ratio of three parts resin to one part hardener. To
this was added fumed silica (Aerosil 200) until the mixture could be
kneaded without sticking to the conservator's fingers excessively.
This calls for the consistency of a soft putty. This fill was then
dyed black using Black Spirit Dye (in dry pigment form). The
resulting, coloured epoxy fill may then be used to fill in the
missing niello on the object in question, employing Industrial
Methylated Spirit (IMS) an a brush to clean up and smooth the fills.
While curing, the fills may be overlaid with Melinex sheeting onto
which a sandbag of similar flexible weight may be placed. Once
cured, polish the synthetic niello with cushionend abrasives and
finish with polishing cream.

This approach yielded very satisfactory results indeed. Good luck,

Hazel Botha
Head Conservator
The South African Institute for Objects Conservation


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                  Conservation DistList Instance 20:45
                  Distributed: Friday, March 16, 2007
                       Message Id: cdl-20-45-008
                                  ***