Molding problem

Troy Mccombs

I made a positive and negative mold of a person/sculpture to use for foam latex appliances. I wanted an extra copy of the positive, so I molded it in alginate and cast it in ultracal (Which I did for the original positive and negative). Problem is, the new positive somehow doesn't fit right in the negative and I can't figure out why. It should fit perfectly, shouldn't it? What could I be doing wrong?

mikenobani4

1. Casting inaccuracy:

Even small shrinkage or deformation during ultracalite casting can lead to dimensional inconsistencies.

It's really important to make sure you are using the correct powder to water ratio for your ultracalite, and follow the manufacturer's instructions for degassing and pouring.

2. Mould damage:

The new alginate positive may have been damaged or deformed during manufacture or storage.

It's a good idea to check for cracks, bubbles, or other defects on the positive.

3. If you've made a mistake when removing the mould from the original sculpture, it can cause problems with the new copy's conformity. Make sure you're using the right solvent to remove the alginate from the original and follow the manufacturer's instructions for mould removal.

It's really important to make sure that the positive is well centred and fits snugly against the bottom and walls of the negative.

Chris Ellerby

Hi Troy,

Alginate shrinks over time, so getting a 100% identical copy would be unlikely.   I would suggest trying a silicone that is rated for minimal shrinkage, as even silicone can shrink a bit during curing.

/Chris