Another way, if all else fails, is to make an air release mould. Of course this does not compensate for undercuts or lack of draft. Also, a release agent is still necessary. Use canvas tube fixed to chicken wire with cable ties, arrange the tube to be an inch away from your mould surface and have one end of the tube closed and the other end hanging out. As the plaster begins to set, cut off the loose end, jam your airgun in the hole and gradually turn up the pressure with your other hand on the regulator. Go from zero to 5psi when the plaster is just discernably warm and increase pressure by 5psi every 30 seconds. If it blows up, do it again but this time go easier on the pressure increase. The best plaster for this technique is ceramic press die plaster but I have done it with other grades such as pottery slip-casting plaster. |