in response to your comment:
David, I honestly don't have any background that helps me to
understand your comment
If you have Time McCreight’s “The Complete Metalsmith”, revised
edition, then please turn to page 182 to see the Silver/Copper Phase
(If you don’t, may suggest that you buy one? Mine is well thumbed.
Might I also suggest Brepohl’s “The Theory & Practice of
Goldsmithing” too, if you do not have it? It’s like having personal
classroom instruction on why we do the things the way we do.)
Let’s return to our sheep.
Notice how the line is ACB is “u-shaped” with the lowest point of
the curve being 71.9% silver and the balance copper. One current
theory* states that you can fuse the granules of a
silver(>>71.9%)/copper alloy onto a sterling or fine silver sheet
without flux so long as it is done in a reducing atmosphere with
free copper because the surface of the granules will have lower
composition of silver (71.9%) and will start to melt before the
interior of granules or the sheet will, all else being equal.
My comment is about what the shape of this curve looks like for a
Silver/Germanium alloy. We know that the melting temperatures for
Silver and Germanium are 961.93deg C and 937.4deg C respectively,
not much room for a u-shaped curve that must drop down to the
solidus zone (light grey). Further, there is only approximately a
24deg C diff between the two elements. My first question is thus,
what is the shape of the liquidus curve and does that curve touch
the solidus boundary?
My next question is whether the above two criteria are both
necessary and sufficient for granulation to take place for any alloy
(reasoning from the specific to the general)?
*what I would like to see both a back-scattered electron micrgraph
and its associated energy dispersive micrograph of a cross section
of a granule fused to silver. If it is true that the copper
composition is higher on the surfaces than in the enteriors of the
granule and the substrate, both micrographs should confirm it. In
the first, the image will have a light surface and a dark interior
while the second should have many more “dots” on the surface than in
the interior when the analyzer is tuned to the Copper K alpha x-ray
No doubt that these images are around, I just don’t know where. Can
any metalurgist help?
ps. I used to do lots of energy dispersive x-ray fluorescence
analysis and electron microscopy in another life.