Silicone Rubber Mold Material, an introduction

Silicone molds are becoming more popular in the craft world and you can very easily make your own. But trying to get information online is overwhelming. There are so many types and kinds of silicone rubber mold material. A trip to the craft store can be even worse because the labels all tell you how great their product is and don’t really tell you how this product is different from the next one. So I’ve done some reading and learning and am passing this information on to you. Here’s what I found about silicone rubber mold material.

What are Silicone Rubber Molds?

Silicone rubber is a stretchy material that is widely used in industry and home use and has become very much a part of our lives. We all use it every day in things ranging from the clear elastic in our clothes to our muffin pans and potholders to the sealants in our bathroom showers. Because of the stretchy nature of silicone rubber and the way that it faithfully conforms to the contours of whatever it is touching when it cures, silicone rubber is widely used in making molds of all kinds, for all kinds of materials, including food, medical devices, theatrical makeup, hobbies, and even polymer clay and jewelry components.

Silicone molds are typically created with something called RTV silicone (for Room Temperature Vulcanizing). RTV silicone consists of two parts that are combined to catalyze a chemical reaction to cause the rubber to “vulcanize” or become polymerized from a very sticky flowing material to a non-stick, stretchy, and durable material. There are many, many types and formulations of RTV silicone rubber mold material, but for craft and hobby uses they are available in two general forms, a pourable silicone rubber and a silicone mold putty.

By the way, silicone rubber is an artificial rubber made chemically from a whole soup of elastomers and polymers. It is not made from natural rubber and therefore does not have the natural rubber proteins that trigger an allergy. So don’t worry if you have a latex rubber allergy, you won’t have any trouble with silicone rubber.

Pourable Silicone Rubber Mold Material

Two parts, A and B, are combined and mixed to create a liquid, pourable molding material. Sometimes the ratio is 1:1 and with other brands the ratio might be 2 parts per hundred. Always read the instructions because every brand is different. Because the uncured silicone rubber is liquid, you will typically find this material used to brush on the outside of a shape to form something called a “glove mold”. Or you can pour it onto a flat item to create a “blanket mold”. A very common use of this material is to form a “block mold” where the item to be molded is placed into a box and the silicone rubber is poured around it, creating a block-shaped mold. Some craft store brands of this material are EasyMold Silicone Rubber, Mold Builder by Casting Craft, and Amazing Mold Rubber.

Pourable silicone rubber typically has an open time (workable time) of 30-45 minutes, depending on the brand, and will be cured and ready to de-mold in several hours time. Different brands vary greatly in their timing, the strength of the finished mold, and their flexibility. For molding small items quickly, though, you might be more interested in a silicone mold putty.

Making molds with silicone rubber mold putty. Learn about the silicone rubber mold material in this article.

Silicone Mold Putty

Silicone Mold Putty is another type of RTV Silicone Rubber Mold Material that comes in a 2-part (A+B) form, but each component is in the form of a putty. The A and B putties are combined in equal parts, kneaded together, and shaped by hand around an item to be molded. This material is readily found in most craft stores and is becoming quite commonly used in both the jewelry and polymer clay arts. This type of silicone rubber has a very short open time, typically under three minutes, and you have to work quickly. It usually sets up quickly as well and your mold is typically ready for use within 30 minutes or so.

You can use most silicone mold putties for food such as chocolate, candies, and fondant. You can also bake food in them, too, as they are heat safe at baking temperatures. You may also use the molds you make for casting polymer clay, resin, precious metal clay, soap, wax candles, UTEE for scrapbooking, and even low temperature metal alloys. Because the molds are non-stick, you can use each one for a variety of materials. You don’t have to make specific molds for each material. Except food, of course. Don’t use a mold for food after you’ve used it for another material.

Many brands of silicone mold putties are available and they have a reputation for being quite expensive. You’d think that mold putty is made of gold or something. Well, it’s even worse. It’s actually made with platinum! Yes, the catalyst for this type of silicone rubber is a derivative of platinum. Who knew? In any event, these types of putty typically cost around $25 per pound, give or take. If you’re buying them in a large retail craft store, though, make sure you print out one of their coupons and get it for 40-50% off. It makes the price much more bearable.

One little factor that is interesting about silicone mold putty is that the cure is inhibited by the presence of tin, sulfur, or amines.  (Some brands will have cure inhibition with polymer clay, too.) This isn’t going to come into play very often, but if you’re having trouble getting it to cure and set up, check to see if this could be the cause of your trouble. If you try to create a mold from something which has sulfur on the surface, for instance, the mold will cure on the outside but the part directly in contact with your object will not cure and will remain sticky.

***Note: It’s come to my attention that silicone putty doesn’t cure very well when you’re making molds from Kato polyclay. There must be something in Kato that inhibits the cure. I found that both raw and baked Kato would inhibit the setting of silicone mold putty. Premo works just fine, though.

An introduction to silicone rubber mold material for crafting use, especially polymer clay and jewelry making.

Brands of Silicone Mold Putty

At my local Michaels store, there are three brands of silicone mold putty. I found Amazing Mold Putty, and EasyMold in the polymer clay section and Mold-n-Pour in the scrapbooking section. Amazing Mold Putty was also available at Hobby Lobby. I recently ordered some EasyMold on Amazon.com for a really great price, too.

Other brands include Alley Goop, Silicone Plastique, and Equinox Silicone Putty, Knead-a-Mold, and Siligum. If it’s a two part putty that you massage together to form a flexible mold, chances are that it’s silicone mold putty. I know that in Europe it comes in many different brand names as well. A lot of small companies buy this product in bulk and repackage it with their own brand name.

From what I can tell, the main difference between the various brands of silicone mold putty is the open time, cure time, and the tear strength of the resulting mold. If you have a specific need, you might need to seek out a certain brand for its characteristics. But if you’re just molding some buttons or small figurines, I think any brand of silicone mold putty will work just fine.

Next, read a comprehensive comparison of Amazing Mold Putty vs EasyMold silicone rubber mold putty.

Also, learn how to create silicone molds from charms. And then learn how to use those silicone molds with polymer clay.

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