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HOW TO "SHRINK" AN OBJECT

You can shrink or reduce the size of an object in all dimensions by using this special mold making and casting technique.


Original model and two shrunken copies

An original model, a shrunken copy made from 1:1 mix, and another made from 1:3 mix

The Castcraft Guides show how to "enlarge" an object using latex rubber molds.

You can also shrink an object in three dimensions by using gelatin molding compound or alginate to cast a duplicate of the object, and then allowing the water in the compound to evaporate. As the water evaporates, the size of the casting will decrease evenly. This is very much like the "shrunken heads" you may have seen where someone carves a head from a fresh apple, and then leaves the apple to dry out, creating a distorted, shrunken version of the head. Using gelatin molding compound or alginate allows you to better control the shrinkage, and allows you to "shrink" existing objects instead of having to carve them anew each time.

Here is the complete procedure to make a shrunken copy of an object:

1) Make a mold of the object you want to shrink. Latex rubber molds are easy to make and will allow you to make a mold of an object with undercuts. You can also use Gelatin Molding compound to make a very quick mold. The "new" Gelatin Compound you use to make the casting will not stick to the cured Gelatin Compound in the mold, but the mold will probably be damaged or destroyed when you remove the casting.

2) Use Gelatin Molding Compound as the casting material. Mix the compound as follows, according to how much you want the casting to shrink:

Powder Amount

Water Amount

Shrinkage

Shrinkage Factor

1 part

1 part

least

.75

1 part

2 parts

medium

.65

1 part

3 parts

most

.55


The shrinkage factor times the original size of the object is the approximate size of the gelatin casting after it is allowed to shrink. For example, if your original object is 4 inches tall, and you make a casting with gelatin compound mixed 1:3 with water, when all the water evaporates from the casting the shrunken gelatin will be 4 inches x .55 or about 2.2 inches tall. The more water you use to mix the gelatin compound, the more your Gelatin casting will shrink, and the more it will distort as it shrinks.

3) Pour the mixed gelatin compound into your mold, and let it set. When the casting is firm, remove it from the mold.

4) Set the casting on some paper towels and leave it in the open to dry out. It may take 2-3 days to completely dry out. If you want to speed the process, you can put the casting in a microwave for 30 seconds or so. Watch the gelatin, and as soon as it starts to steam, turn off the oven. You can repeat this procedure over a period of a few hours until the casting is mostly dry. Another alternative is to put the casting in an oven turned on very low (about 175 F) and leave it for a few hours.

5) The gelatin will shrink quite evenly in all dimensions, and should make a good, but smaller, reproduction of your original object.

Gelatin castings that shrink a little bit (a 1:1 mix) will generally be more accurate than those that shrink more. Gelatin castings that shrink a lot (a 1:3 mix) may have some distortions or warped areas.

If your dried, shrunken casting is warped or distorted, it is easy to fix:

High spots can easily be carved down with a sharp knife, or sanded with sandpaper.

Low spots or air pockets can be filled with wood putty, clay, or spackle.

6) Once you have a good casting in the size you want, give it a couple of coats of clear spray sealer such as "Krylon" clear acrylic spray. Then you can make a rubber mold of the shrunken casting and make as many reproductions as you want, in the material of your choice.

7) If you want an even smaller casting, you can repeat the process as many times as you want - make a mold of the shrunken casting, cast gelatin into the mold and allow the casting to shrink, make another mold, and so on.


Download a PDF source list

Includes 26 suppliers of all mold making and casting materials mentioned in ALL the demonstrations on this web site, including silicone rubber, polyurethane rubber, latex rubber, polyurethane plastic, epoxy resin, polyester resin, molding clay, foam board, release agents, pottery plaster, Hydrocal, metal powders, other plastic resin fillers, and gelatin molding compound. With company names, addresses, phone numbers, and web sites. Downloads to your computer as a PDF file.



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