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Niello and Fire-gilding


#1

Hello,

I am studying some carolingian strapends and buckles. They have
traces of gilding and they are inlayed with niello. At the moment the
places were the niello is are not gilded, but is seems very well
possible that the gilding is worn of at this points since they are
always the highest points of the objects.

Thinking about how they may have been produced I began to ask what
the order of working could have been. Did they first fire-gild the
object and then inlay the niello? In that case they would be forced
to file and polish off some (or all) of the gold when finishing the
niello inlay. But if they first did the niello inlay, would it be
possible to gild directly next to the niello, without covering the
niello? It seems that on a lot of objects there is no gilding
directly next to niello. If have been searching around to find any
answers to this question, but couldn’t find anything so far. I hope
any of you can help me.

Regards,
Janneke Zuyderwyk
archaeology student,
University of Amsterdam,
The Netherlands


#2

Hi Janneke,

From the descriptions of the processes by Benvenuto Cellini - The
object would first be inlayed with niello. Then, the niello and areas
not to be gilded would be painted with a resist made of either
fuscello (a flour and water paste), or a paste of fish or stag glue
(a hide glue) and gesso. Then, the piece would be gilded.

For more in depth look at The Treatises Of Benvenuto
Cellini On Goldsmithing And Sculpture; Chapter 1 On The Art Of
Niello, Chapter 26 How To Gild, and Chapter 33 What You Do When You
Wish To Leave Bare The Silver In Certain Places.

Best regards,
Lyn


#3

From what’s in On Divers Arts by Theophilus

http://www.ganoksin.com/jewelry-books/us/product/0486237842.htm

which was written in the 11th century, I would hazard to guess that
they would inlay the niello first, then apply the mercury amalgam
gilding. The niello would be fused in the 500-600 degree F range, and
the gilding could be set a much lower temperatures.

I’m not really sure the amalgam would even stick to the niello (I
have no idea how the mercury would react to the silver and copper).

While I suspect the effect you see is from wear, it’s not beyond
belief that the exposed silver was a deliberate contrast with the
gold and niello.

Ron Charlotte – Gainesville, FL


#4

Hello Janneke;

... Did they first fire-gild the object and then inlay the niello? 

Without seeing the articles, I can only speculate on a couple
approaches. It is possible to apply niello to an article that already
has already been gilded, but probably not the other way around. The
melting temperature of the niello is low enough that if there were
any proximity to an amalgam paste containing mercury, you’d get a
mess as the two compounds reacted to each other.

As to the problem of grinding away the gold after niello inlay,
niello can be ground to a powder and inlayed much the same as glass
enamels, that is, carefully filling the areas, melting by heating the
entire article, then repeating the process until a level surface was
attained. It would then even be possible to burnish the entire
surface, if the niello alloy had sufficient lead content to be
slightly malleable, which would tighten up the visual effect of one
color metal meeting flush with the other, everything at the same
level.

On the other hand, careful and practiced technique could suffice to
make it possible to finish the surface by a technique I’m reluctant
to divulge here on Orchid (I know, shame, shame, but why shouldn’t I
get a chance to get some credit for this skill before everybody is
doing it?). I have inlayed neillo in patterns as shallow as 1/100th
of an inch, overfilling and removing down to level with the metal
being inlayed, without appreciably removing any of the metal the
niello is inlayed into. Obviously, if you’ve only got 1/100th of an
inch to spare, you’d need to know how not to obliterate the pattern.
And mercury (a.k.a. “fire gilding”) can be applied thicker than this.

Now a second scenario, albeit briefly. Are you able to establish
with certainty that the gilding was fire gilded? Is it possible the
gold is actually inlayed into the niello? Certainly possible by
physical means using the right niello alloy and very high karat gold.
What is the base metal of the article? Many ancient craftspeople knew
that gold would bond at very low heat if it were close to pure and
the metal article was silver with a purified surface of fine silver.
Consider the Keum Boo technique often discussed here on Orchid.
Finally, there is an applique technique for mechanically binding gold
to other metals that doesn’t use heat at all, such as the Japanese
used in their work. Again, without seeing the article I am only
supposing.

David L. Huffman


#5

Dear Lyn, Ron and David

Thank you for your help! But unfortunatly also from you i get
’contradictionary’ answers. Two go for niello first and then gilding,
one the other way round. Best would be to experiment myself, but this
will be impossible with fire-gilding since it is to dangerous to the
health.

David, can you explain why niello would react with mercury?

From someone else i understood that goldamalgam would not bond at all
with metal sulphides.

Thanks,
Janneke Zuyderwyk


#6

Hello Janneke;

David, can you explain why niello would react with mercury? 

I’m a metalsmith, not a metalurgist, so I can’t explain the technical
stuff about eutectic phenomenon, although I’m sure someone here can.
Basically, what I’m referring to is this; when you heat two metals in
proximity that have very different melting temperatures, and mercury
is molten at room temperature, the metal with the lower melting
temperature will dissolve away the other metal, as at the contact
point, a new alloy is being created that has a melting temperature
somewhere between the two parent metals. That is essentially why the
mercury guilding works. As for metal bonding, there are a couple of
conditions present. When a low temperature metal melts on a higher
temperature metal, such as lead solder on copper, it is essentially,
at first anyway, a mechanical bond, the low temp metal penetrating
and locking into the surface of the other. At some point of
temperature, the metals begin to alloy together, mixing molecules to
form an alloy. Also, I don’t know if gold amalgam would stick to
niello, but I suspect it would. I’ve applied niello to gold, silver,
and platinum. It is, again, the kind of bond that lead solder makes
with copper. It won’t stick to some things like steel very well, but
I’ve done it. Short of performing dangerous testing using mercury,
I’m still giving you hypotheses, and from my limited metalurgical
knowlege at that.

David L. Huffman


#7

Hi Janneke,

I think you’re getting contradictory answers because we’re all
working on hypotheses. I’ve worked with niello, but as you said,
fire-gilding is way too dangerous.

My hypothesis would be that the gold amalgam and niello would stick
and create a mess. I think there’s no gilding directly next to the
niello in the Carolingian pieces because the niello was covered (with
a paste that Cellini describes how to make) before being gilded. I
used Benvenuto Cellini as a source because he gives very specific
details, on how to niello, how to cover areas you don’t want gilded,
and how to gild.

Also, looking further into your question I found this research
article:

The Composition of Niello Decoration on Gold, Silver and Bronze in
the Antique and Mediaeval Periods W. A. Oddy, M. Bimson, S. La Niece
Studies in Conservation, Vol. 28, No. 1 (Feb., 1983), pp. 29-35

You can go through your University library and get a copy of this at
jstor.org. The article gives analytical results for 18 niello inlays,
and confirms on one piece that the niello was inlaid before the
object was gilded. However, it doesn’t explain why it was done in
this order, if the niello and gold amalgam would bond, or if there
was any evidence the niello was covered before gilding.

So, even though it answers your question about the order of the
processes, it doesn’t answer any of the metallurgy related questions.

Best regards,
Lyn