Best Molds for Pouring Molten Silver: A Comprehensive Guide

Question
to prevent air bubbles when pouring molten silver into the mould which type of mould can be used?

Answer
hello Yogananda
the only moulds you can direct pour into are cuttlefish, Tuffa stone, plaster (investment), or firebrick. All the other  compounds will melt. coating your wax with a debubblizer solution greatly decreases the  porosity- you can use alcohol  too for a debubblizer-just ensure the applicator leaves no fibers or  hairs on the piece( cotton swabs, or a paintbrush are the easiest methods of  applying it to the wax or  master). If you are getting bubbles  chances are you are not letting the investment  burn out long enough and there is still moisture in the investment ( a plaster  compound). also  vibrating the  investment in the flask is  another method of getting the most  bubbles out of the investment as is possible before burning it out.
Delft clay works with silver  too but is far easier  if you  direct pour into  a tuffa or cuttlefish mould- with the delft clay you have to develop a skill for the  cope and drag method  which , if too dry crumbles when you  place your registration marks and sprue into the  mould- and if too humid or the clay too wet will not cast without bubbles all over from gasses pushing against the surface of the mould.A lot of work  for a risky outcome-I would highly recommend trying your hand  at carving directly into cuttlebone and making a mould  with it as opposed to clay as a starting point. African traditional mould making uses small amounts of plaster of paris poured sequentially to develop a shell-like coating around the piece until you develop a sprue and pour spout  built by layers of plaster poured and dried until you create a shell of sorts around the piece.Carles Codina  discusses this method in his book Goldsmithing at  length. It  is  tricky and like  all the  other direct casting mould methods the mould is  good for only one use.
If you do decide to try cuttlefish casting  go to a pet supply store and ask them to order a box  of  jumbo  cuttlefish bone for you- it  will cost far less than the 25  dollars or so (USD) for 6 pieces..In India they  collect the bones on the beach- it is free if you are close to the coast and easy to prepare as they sundry and  are  essentially ready for use once cleaned  up slightly. If you need a source for the bones I have  one that  sells it by the 50 gallon drum- depending on where you are in the world- I find this the cheapest way to buy. The only limitation to that source or any Indian supplier is that once the gathering season is over there is none until the  following year.
I hope this helps, if not write me again and I'll clarify anything  you need  more help with. I also recommend Tim McCreight's book "Practical Casting" .It can be had on  amazon .com, alibris.com or abe books.com, among other  on-line sources  starting at 2 or 3 dollars for a used copy..
Best regards,Ari