How to make your alginate molds last longer
You can mix up to 2:1 Distilled Water and Glycerine together in a container and then mix this with your alginate. I know people who claim to be able to use a 1:1 water to glycerine ratio and they say it works just fine. I haven't tried it - yet. Always remember to add the alginate to the water and not the other way around.
Since glycerine is hygroscopic (retains moisture), the alginate lasts longer and helps reduce shrinkage. This in turn allows your pour to be more accurate. If you are using clay to make your positive, be SURE you have zero standing water or drops of water in the alginate when you pour! If it's a stone product, a little moisture won't hurt, but try your hardest to get it all out.
To dry the inside surface of the alginate, you can spray or rinse the surface with acetone. USE ADEQUATE VETILATION WITH THIS TECHNIQUE! As soon as the acetone flashes off, you can begin casting.
With this process, your alginate molds can last for hours uncovered without any shrinkage. Some may even last a day or two with minimal shrinkage.
I mix my alginate to the consistancy of sour cream. If you make it too runny and thin it can actually promote shrinkage because of the higher water content. The best water to use is Distilled Water. There are too many impurities in most municipal water systems to use for mixing alginate.
Most of you probably know this info already, but you never know when a little "nugget" of information might help someone down the road.
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