Jack Schmidling wrote:

I am having big problems casting a simple cup in fine silver. I have
attempted to pour this about 10 times and they all look more or less like
the picture I have posted. I have tried much higher than normal temps,
increasing the size of the base, buttresses in the sides, longer spure
with
a 1/4" gate and nothing works. I have tried sterling and fine silver and
get the same results.
(...)
js

Possibly gas or steam? Too hot, sand rammed too dense, damp or dirty sand?

Jack Schmidling wrote:
I am having big problems casting a simple cup in fine silver. I have
attempted to pour this about 10 times and they all look more or less like
the picture I have posted. I have tried much higher than normal temps,
increasing the size of the base, buttresses in the sides, longer spure with
a 1/4" gate and nothing works. I have tried sterling and fine silver and
get the same results.

I'm no expert on this, especially with precious metals. But, I wonder
if the weight of the silver is causing the sand to collapse into the
mold cavity. What are you using to bond the sand?

I've never even heard of sand casting precious metals. Most people use
investment casting. You still use the flask and sand to support the
fragile investment. But, the hard investment keeps the sand from coming
apart and contaminating the metal, as well as it keeps the mold cavity
open.

Jon

Jon Elson wrote in message ervers.com...
Jack Schmidling wrote:
I am having big problems casting a simple cup in fine silver. I have
attempted to pour this about 10 times and they all look more or less like
the picture I have posted. I have tried much higher than normal temps,
increasing the size of the base, buttresses in the sides, longer spure with
a 1/4" gate and nothing works. I have tried sterling and fine silver and
get the same results.

I'm no expert on this, especially with precious metals. But, I wonder
if the weight of the silver is causing the sand to collapse into the
mold cavity. What are you using to bond the sand?

I've never even heard of sand casting precious metals. Most people use
investment casting. You still use the flask and sand to support the
fragile investment. But, the hard investment keeps the sand from coming
apart and contaminating the metal, as well as it keeps the mold cavity
open.

Jon

I couldn't find the original thread, but you can sand-cast precious
metals just fine. Yes, investment casting is the common process now,
but many jewelers used to sand-cast or cuttle-fish cast simple pieces
before the process got adapted from the dental trade. Since I didn't
see his picture, can't tell what might be the problem, but to hazard a
guess, if it's a porosity problem (as most casting problems are) the
culprit is either disolved gas or too coarse a casting sand. I cast
small items using the so-called "Delft clay" material, which is really
fine oil-bonded casting sand. Silver is notorious for absorbing gas
when molten, which then bubbles out as the metal solidifies.
Over-heating the metal makes it worse, as does not keeping the melt
covered at all times with a reducing flame, including pouring
**through** the flame into the mold.

A cup should be pretty easy to do as a sand casting.

Jack -- if you post the link to your pics again, I'll take a look and
see if it looks familiar...:-)

Regards,

Bob