I was wondering if someone can help me out. I want to cast some
sheet silver, on a very basic level. I heard that you can use
plaster for the mould, which you let dry out completely, and then
pass a flame over the surface of until black. It’s then ready to
pour the molten silver in. Based on that I want to
carve in to the surface of the plaster mould, so that the resulting
sheet has protruding marks. Any tips on heating the scrap silver in
a crucible? And on making the plaster mould for the sheet. Can I
just pour the metal on to the carved block of plaster? I’m not too
concerned about achieving perfectly flat sheet. I want a very
primitive effect.
Many thanks, in anticipation,
Rebecca, Liverpool, UK.
Rebecca: Don’t do it!! Unless the plaster is formulated for high
heat and has been baked for a considerable length of time in a
oven it will still contain water. When the hot metal hits the
plaster the water will be released as steam and you will have a
miniature volcano. Hot metal (red hot) will fly through the air and
land in the most unfortunate of places. Like on you… If you want
to pursue this technique try cuttle bone casting. Two pieces of
cuttlebone are wired together after the pattern is carved into the
surface. Molten metal is then poured into the pattern through
channels carved into the cuttle bone. Not to dissuade you from your
creative process, but when dealing with molten metal KNOW what you
are doing before you try experimenting. The results of lack of
knowledge combined with 1800 degrees plus of hot metal can be very
dangerous. I suggest you take a few classes or do some really
serious reading before you continue your project. Frank Goss
I’ve considered cuttlefish casting, but I need large areas of sheet,
possibly up to 30cm x 20 cm. It seems I might not be able to do
this then. Maybe I’ll get in touch with an industrial company who
cast sheet, and see if they have any ideas.
I've considered cuttlefish casting, but I need large areas of
sheet, possibly up to 30cm x 20 cm. It seems I might not be able
to do this then. Maybe I'll get in touch with an industrial
company who cast sheet, and see if they have any ideas.
Have you investigated sand casting? I don’t have any experience with
sand casting but I’ve been around people who do and they use it for
casting blades, making the models from wood and packing the sand
around it, removing the model, then pouring the molten metal into the
sand mold. Seems you could make a “sheet” from wood pack the sand,
then make your markings in the sand afterwards. I believe the Tim
McCreight casting book (?) has some info about sand casting.
Frank’s answer is correct to a point. Plaster molds are a viable
technique used industrially. They are usually used for zinc and
aluminum casting but occasionally are used for bronze and other
copper alloys. I use them as cores in sand casting bronze as well as
cores in ceramic shell investment molds. The Plaster can be molding
plaster about 50-50 with fine sand or any plaster investment
material. I use molding plaster with 60 80 mesh silica sand.
Idealy you would use an entraining plaster mix but I haven’t. The
molds MUST be baked to remove Water before casting and used quickly
because the material will pick up water again after it cools. Molds
for aluminum and other lower melting metals are baked to 400- 500 F
to be useable. Molds for bronze and higher melting metals ( which
would include silver) are baked to what would be normal investment
casting burn out temperatures - 1200F would be a normal maximum
temperature but 900 F would be OK and risk less damage to the
plaster. 900 F wax burn outs cast in bronze have been found to be
very satisfactory. Your mold would not have wax to burn out but
the 900F temperature should be reached. You can expect some
small porosity in what you are planing . Black discoloration on the
surface if any will be the result of breakdown of the gypsum
plaster - a sulfur compound. Depending on the size the mold is very
simple and will look like a small version of a mold to make wax
sheets for wax sculpture to be investment cast in bronze , or
whatever. Start with a flat non porous surface - wood, glass a poly
cutting board or the like . Lay a sheet of a similar material
thicker than you want as big as you want on top of this and build a
retaining box around this with a little space for a plaster wall to
form. cardboard , tape or even plastiline works. coat the surface
to be coated with a mold release such as Pam, vegetable oil, wax or
a silicone compound - I use silicone "tire shine"from an auto parts
store . Mix you plaster mix. Pour in - let set. Remove mold box .
Turn over the mold and carve any details in the surface . Proceed to
dry out the mold . The cores I use in bronze sand molds have only
been baked out to kitchen oven temperature,and kept in a sealed
metal can until use a few hours later- this is not ideal but if the
core is vented well they work great. In ceramic shell molds the
core goes to the burnout and vitrification temperature just before
pouring.These cores are also installed so they re well vented to
get rid of any gas formed by the hot metal. These really work well
at bronze temperatures. I have reused this type open mold several
times for pewter but at the higher temperatures they are considered
one time use. You should have some experience with the casting
techniques and the requirements for safe handling. jesse
I've considered cuttlefish casting, but I need large areas
of sheet, possibly up to 30cm x 20 cm. It seems I might not be
able to do this then. Maybe I'll get in touch with an industrial
company who cast sheet, and see if they have any ideas.
When Barb mentioned sand casting, that got me to thinking about
Delft clay.
If you got a a metal baking pan about the size you need, you may be
able to pack the clay into it & impress or carve the desired
inscription in the clay.
I brushed over rather lightly yesterday what probably is the biggest
problem you face. That is porosity. Molten silver can adsorb a
tremendous quantity of oxygen - about 20 times its volume. as the
metal freezes it can no longer hold this and the gas escapes. This
will create a very porous surface particularly on the top or where
the metal freezes last. This problem would be alleviated by using a
material other than standard copper based sterling and or handling
in an oxygen free atmosphere. There is a germanium -silver alloy
that is supposed to be deoxidized enough by the germanium so that is
free of this porosity. I haven’t used it and haven’t handled nearly
as much silver in one pour as this piece (20cm by 30 cm) would take.
A flux cover and maybe a graphite mold would be needed . Copper has
some of the same problem to a lesser extent- in this case the
silicon bronze alloys handle the problem quite well. The preferred
one being Everdure bronze which is copper with 4% silicon as a
deoxidizer and property improver. This would be a preferred alloy to
cast. You may want to consider silver plating a bronze casting if
you don’t mind not being a purist. Someone casting bronze
plaques could do this for you quite easily from your pattern. jesse
Good day. I have been following this tread with interest. Some 20
years ago during a remodel of my house, I needed a special
electrical box flange. I had one flange, but needed another. It
was about 4 inches in diameter and � inch thick with various holes
and protrusions. This was prior to becoming hooked on
metalsmithing and jewelry. I had a method of melting aluminum and
had heard of sand casting so I thought I would give it a try.
I took very fine sand and made an impression from the existing
flange, it did not hold detail as nothing bonded the sand. I next
tried wet sand with impressive if not effective results when the
molten metal hit the damp sand!
I next turned to plaster of paris. I molded the part, removed it and
let the plaster of paris dry for a day. When I poured the molted
metal in, I found that it still had a lot of water in the plaster,
and metal again spewed all over. I did the mold again, but this
time I put it in my home oven at 500 degrees F for a couple of
hours, then while it was still hot, I poured the aluminum (melted
beer cans, and scrap metal) into the mold. It worked great! A
little shrinkage as it cooled, but very usable.
Silver melts at a higher temp than aluminum, so it may act
differently, and knowing what I know today, I would not use plaster
of paris when casting mix is so readily available.
Cast metal also has a different grain structure and does not seem to
work as well as metal that is forged or worked.
Have you considered using sheet wax and the lost wax casting
process? I assume that the size of sheet needed would not work but
this would be great for smaller pieces thicker then 0.2 mm. I
personnally use an ingot mold hammer it down a bit and pass the ingot
through my rolling mill(takes me many hours). This is how most people
make sheet from raw material and CLEAN scraps(i.e. no solder or
contaminants). My prefered method is picking up the phone and
contacting Imperial Smelting(Canada) and ordering beautifull shiny
sheet to exact specs Saves my wrists for golfing.
This is more a question than an answer to the problem of casting
sheet silver, but could one make a mould out of investment, dry it in
the oven or kiln, and then pour silver into it ?? If it worked it
would would give a nice smooth surface which one could carve or just
let be. Just wondering.
I haven’t followed too much of this thread - excuse me if I duplicate
info- a reply from “Jon” said it best- why not just pick up the phone
and order some? There is something else related, too. If you cast
sheet metal, you won’t really exactly have sheet metal, you’ll have a
cast plate. Sheet metal is what it is because of the rolling
process, which packs and elongates the grain structure - plus
commercial sheet is milled before it’s rolled - that’s why it’s so
perfect. Then there’s the issues of casting it at all - in order to
get a 6"x6" sheet, it’s going to have to be something like 10 or 12
ga. at least for the metal to fill, and you’ll need a 7" flask, and
machine, to do it. And then there’s porosity
Saves my wrists for golfing.