Custom Mold Making

Tips and Tricks

Plaster Ratio

Master Mold Mix 

Water / Plaster / Total

  6           10         16

   9           15          24

 12           20          32

 15           25          40

 18           30          48

 21           35          56

Production Mix

Water / Plaster / Total

  7          10           17

10.5       15           25

14          20           34

17.5       25           42

21          30           51

24.5       25           59

28          40           68

Mixing Plaster 

Add your water to the bucket first, then your plaster,  allow the plaster to set in the bucket for a few minutes to soak up the water, you'll get a better mix this way.
Mix your plaster for at least 30 seconds using a low speed drill so you do not force air into the mix.

Measuring for Rubber

Measure the inside of your rubber box, length x width x height of mold x .03645  
This will give you a close estimate of the rubber needed for your rubber block

Soaping your mold

Soap your mold heavily and allow it to set on the mold for 10 to 20 minutes, gently wipe off with a wet sponge or rinse under the sink using warm water, repeat 2 to 3 times just to make sure the mold is sealed.
If your preparing your mold for a rubber block do the same process, but after the last rinse make sure you remove all the water before pouring rubber.
Using Vaseline

You can use a thin coat of Vaseline on any porous model before pouring plaster, if the piece is glazed vaseline would not be required.
Do not use vaseline if you're pouring rubber over your mold, it will not seal the surface as well as mold soap, and air my be released from the mold ruining your rubber block.
Is it better to glaze my bisque before I make a mold?

No, once you glaze your bisque you will lose a lot of the detail. 
it's best to apply a thin coat or Vaseline to the bisque.

If you're making a mold of a piece with little or no detail such as a plate or bowl, then yes a glazed piece will work just fine, and it will not require any Vaseline.