“Hi” Allan I have used the delft clay casting and had good
results as far as fine detail is concerned.
I have met the gentelman who developed the system while in
England a few months ago, in fact it was at the International
Jewellery Fair at Earls Court where he was demostration the
technique and had done about 400 castings during that time.
Because the clay has a special oil that bindes the particals of
clay together and which stops the gases escaping through the clay
you need to have good venting from your mould cavity.
In watching him do several casting I learnt some good points. 1.
He used the face of an engineers hammer to pack the clay into
both of the mould rings then leveled it of with a steel rule. 2.
Use a talc powder as a parting agent between the two halves so
they will come apart easy not too much. 3. Make good vents from
the mould cavity by drilling 3 or 4 holes around the top half of
the moulding ring then cut into the clay a channel just deep
enough (to allow the gas to escape)and to match up with the
holes. To give extra venting around the mould cavity push a wire
say 28g about 3 m/m from the edge of the cavity through to the
outside of the mould taking the wire right through. Do this all
the way round the shape of the cavity. Venting is the secret to
the process. 4. 1f you have a large volume of metal make sure
that you have a weight on top of the mould assembly to stop the
top from floating off. 5. Make sure that you have a large enough
entry to the mould cavity not only to make it easy to pour but
also to allow for shrinkage. The casting that I watched him do
several times was a medal which had engraving in the centre of it
and came out just as well as the one he was using as a pattern.
The top of the pouring hole can be tapered to give you a large
button to alow for shrinkage.
Hope this is of some help. E-mail me if I can help in any other
Major Boyce @pyramid