Have you ever used cookie cutters with special little designs imprinted? You press the cutter down onto the dough and it leaves an exact opposite of the design you see in the cutter itself.
That's actually a mold.
A mold is something you can use over and over to replicate a design, shape, form. Think of the mold as the negative that forms your positive.
A master block is actually the permanent positive for your mold. From the master block, you can make numerous molds and from the mold, you can replicate numerous positives in the finished form.
Place your hand down onto rolled out dough and make a print. Your hand is the positive-the print in the dough is your negative.
If you happen to want numerous copies of an original, you will need a mold. From the mold, you can make 'repeats'.
If you also happen to need to know that you can make numerous molds, all exactly the same as the original mold, you will then need to freeze that design for all time, by making a master block of the original mold. In this way, you can continue to make the same exact mold, over and over for years. Thereby, freezing your design for all time.
Different types of molds
When people think 'mold making', it's very possible they wind up in all the wrong categories because they were thinking one thing and the search engines are coming up with yet a whole other item.
When it comes to making molds, there is a wide variety of types and uses. I thought I'd take some time to help clarify.
First, we look at the many types of materials one would use to make an object from a mold. Objects can be made from plasters (I say plural because of the many varieties of plaster and their uses), clay, resin and paper. Yup...paper. Well, there's also glass but we're pretty much sticking to things that can be formed without a furnace. There are also different metals, one can use.
For the most part, folks are trying this out at home so we will look at those forms that can be done on the kitchen table (if need be).
Molds to form items out of plasters, are made of rubber. Of course, you can make a plaster mold to turn out plasters but rubber is so much easier to live with.
When trying to decide which rubber to use, check for flexibility and release. Flexibility becomes important when you may or may not be using a mother mold. A mother mold is sort of a rigid backup, to hold your rubber mold in place. Like a cradle.
Release is important when you are making objects made of resins. Some rubber compounds come already formulated with a self release. It's sort of 'greasy' on the surface, all the time.
Especially with rubber compounds that aren't already self releasing, you will need something called 'mold release'. For rubber molds, this mold release is usually silicone but there are others and you need to make sure your rubber molds are compatible with the release.
Liquid latex molds are a 'build up' mold. It's created by layering coats of the rubber onto the object being copied. Enough layers, and you have a sturdy mold.
Molds made of plaster also depend on what type of object you care to reproduce, as to which type of plaster to use. Most times, it's just pottery or #1 pottery plaster (also known as plaster of paris).
For very large objects made from a plaster mold, I would suggest hydrostone instead. It's much denser and harder than #1 pottery plaster. You can make plaster objects using a plaster mold only if there are no undercuts to trap the object.
Another material I love using is called hydrogel. It's actually made from seaweed and harmless to the skin. Great for making forms of the human body. With hydrogel, one must immediately add on top of the soft new mold, a mother mold of plaster, in order to hold the hydrogel in form, as it is soft and pliable. Also, hydrogel molds can only be used once and pretty much immediately as the material dries up quickly. As it dries it shrinks and contorts.
This should give you a ballpark view of the different kinds of molds, materials and the uses.
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