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Making niello - an immodest proposal


#1

Hi All,

    It  probably would be worth a try the temps are not too high to
deal with. Dose anyone have an idea of the relative amounts of each
sulfide in nellio? 

in response to my comments on using sulfides directly rather than
creating the niello from the elements. My sources are McCreight, T.,
“The Complete Metalsmith” (1991) and the CRC Handbook of Chemistry and
Physics (HCP).

Question, can niello be made using the metal sulfides? I simply do not
have the resources to test the idea out. Besides, even if I did, I
live in a condominium and doubt very much that my neighbours would
appreciate me being a latter day alchemist. Anybody out there who is a
school teacher of college instructor with access to a chemistry lab
willing to try this out?

Below is some base data. Although McCreight expresses the recipes in
ozs we can use any units of measure we please because all of the units
use a common base. Therefore we are looking at the proportions of
elements used to make up niello.

Part 1: What are the relative proportions of the metals in atoms that
make up Niello? Let’s start with silver (Ag) and copper (Cu) using
Heinrch’s recipe. We see that the proportion of silver to copper to
lead is 1:2:3. That does not mean that we use one atom of silver to
two of copper and three of lead. The weights of the three elements are
very different from one another as shown in the table. The relative
weight of one silver atom is almost twice as much as an atom of
copper, for example. But because we are going to convert our elements
into molecular equivalents, and because each compound can have
different relative number of atoms we need to convert the mass units
in relative numbers of atoms.

Take the recipe Augsberg #1 for example. To make this niello we
require 1 gram of silver and one gram of copper. This means that we
require 9.3 atoms of silver to 15.7 of copper. These ratios are messy
and they can be converted into whole numbers by dividing each line by
the smallest number and round to whole units

	Element		Ag	Cu	Pb	S
	A.W.	    	107.87 	 63.55 	207.19 	32.06 
	M.P. deg C	962 	1,083 	327.5	
	
	Recipe as mass units				
	Fike		6	2	2	6
	Heinrich	1	2	3	6
	Augsberg #1	1	1	2	8
	Ruklin #1	1	2	4	5

	Recipe expressed as proportion of atoms				
	Fike	      	 55.6 	31.5 	9.7   187.1 
	Heinrich	  9.3 	31.5   14.5   187.1 
	Augsberg #1	  9.3 	15.7 	9.7   249.5 
	Ruklin #1	  9.3 	31.5   19.3   155.9 

Recipe expressed as relative number of atoms (rounded to create whole
units)

	Fike	           6 	  3 	   1 	   19 
	Heinrich	   1 	  3 	   2 	   20 
	Augsberg #1	   1 	  2 	   1 	   27 
	Ruklin #1	   1 	  3 	   2 	   17 

Part 2: Given the relative number of atoms we require what relative
masses of sulfides do we need? There is only one compound of silver
sulfide (but found as two minerals), whose formula is Ag2S (I can’t
create a subscript in my Netscape word processor). Copper sulfide
exists as two compounds, Cu2S and CuS, the latter transforming at 103
deg C. So I chose Cu2S. Lead sulfide exist as a single compound.

Let’s take the recipe for Augsberg #1. We have discovered that to
make niello using this recipe we require one atom of silver to two of
copper. If we combined an equal number of molecules of Ag2S and Cu2S
we would have a mixture with the ratio of Ag to Cu of 1:1. This is not
what we want. We want the ratio to be 1:2. Therefore if we take 1
molecule of Ag2S and 2 molecules of Cu2S we will have 2 atoms of Ag
and 4 atoms of Cu in the ratio of 1:2, just what we want.

	Atoms as sulfides Ag2S	Cu2S	PbS	
	M.W.	      	 247.8 	  159.1   239.0 	
	M.P. deg C	 825 	1,100 	1,114 	
	atoms of metal     2	    2	    1	

	Recipe expressed as relative mass of molecules				
	Fike	       	743 	  239 	   239 	
	Heinrich	124 	  239 	   478 	
	Augsberg #1	124 	  159 	   239 	
	Ruklin #1	124 	  239 	   478 

Now let’s see how much lead (Pb) we require. We need only one atom of
lead. Using the same logic as before we can see that we need one
molecule of PbS. Now if we can imagine that we could handle each
molecule of the sulfides independently we could combine them in the
proper ratio. But obviously we cannot. Further we discover that the
molecules have different weights. Ag2S weighs 247.8, say, grams while
the same number of molecule of Cu2S as silver weighs only 159 grams.

Therefore we must now convert our proportion of molecules to mass
equivalents by multiplying our proportions by the molecular weight of
the compounds. Hence in the case of Augsberg#1 the mass equivalents
aRe: Ag2S - 124 grams, Cu2S - 159 grams, and PbS - 239 grams. Of
course we could divide the weights by 10 to work with more modest
amounts.

Part 3: Making the mixture Next I propose that the materials be ground
as fine as possible to increase the surface to volume ratio so as to
assist in fusing (pure speculation based on empirical observations of
melting sugar in water). Next (and I have absolutely no fact to
support the next step, just intuition), I would melt the silver
sulfide in a crucible first because it has the lowest melting point. I
would then add the copper sulfide second hoping that it would dissolve
in the melt. Next I would add the lead sulfide. However, the physical
properties might be that lead should be added next, I don’t know and
would have to discover empirically which process is the more
effective.

In the Middle Ages an Apologia was written at the start of the text.
So I am backwards here. I have no idea if fusing the sulfides will
work or not. I am hoping that it will. When sulfur is heated in air
some of it combines with the oxygens to form sulfur dioxide and when
this sulfur dioxide is disolved in water it forms sulfuric acid. That
is why in part the fumes are so nasty, there is sufficient water in
the lungs to make sulfuric acid. In addition, metals when combined as
sulfides are not all that biologically available, meaning that heavy
metal sulfides are comparatively safe to handle. Given these two
circumstances I am hoping that someone will test out the idea
expressed here. It might save a lot of people grief and permit the use
of niello, this really exquisite material, to be used more often.

Regards,

David