FreeShip- Castor Oil, All Purpose Release Agent for Natural Latex- (Prompt rebate on orders with 3 or more FreeShip items!)

DESCRIPTION-> Click "Learn more about this item" for article & instructions!
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This interesting oil is used extensively as a release agent for latex molds and is also used to make "Turkey Red Oil"! I could not resist in leading with a reference to that famous (?) product. (See more at the description's tail end!). This oil is the one to use when you're making and working with latex molds. It has been used for about the last 90 years as the mold release agent of choice for natural latex molds. It's a low solvency vegetable oil that actually conditions and maintains the latex mold surface contributing to mold longevity. Since a latex mold is not self releasing like silicone molds, it does need a release agent. You should be aware that other oils and release agents, even ones designed to release specific casting materials from all mold materials can actually degrade latex, causing it to break down. Release agents or oils having hydrocarbons (petroleum or aromatics), oils derived from crude oil (petroleum) or aromatic solvents from some plants and animals will degrade latex rubber significantly. Good latex molds can last for many pulls and many years if properly cared for. Release agents are right up there among the factors that determine how long a latex mold will last.
The following description of using castor oil on a latex mold includes some information on latex molds themselves, and has some references to the way latex molds are made that you may not understand. See the description of one of our latex rubber listings, such as Latex.75 to help you round out your understanding of latex molds.
Since latex works best with certain casting materials and not so good with others, the casting material you pour into your latex mold also has a significant effect upon how long the mold lasts. In particular, resins and hot materials such as waxes do not do well in latex. A bit about why that's true:
To successfully cast resin in a latex mold you need a strong barrier coat besides a release agent. PVA (polyvinyl alcohol) works well. When it's applied to the molding surface in a thick coating and dried, a release agent such as a silicone-based spray release will afford about the greatest protection you can get from resins attacking the latex surface. Even so, that barrier will only protect the latex from resins for a limited amount of castings, perhaps 10 to 20 more or less. You can get hundreds of castings from a latex mold with casting materials that are cementitious, when molds are cared for properly (and made properly). The low amount of castings you can get with resins also holds partly true with materials that are hot (low temp paraffin candles would work best). The same barrier coat and release agent used for casting resins also works about as well for hot casting materials such as certain waxes and again, resins (solid resin castings generate exothermic heat up when curing, if you can eliminate that heat by making hollow resin castings that would help give you more resin castings; not needed if your resin castings are very small).
As mentioned above, cementitious casting materials do quite well in latex and are used by far the highest amount on a tons per year basis when cast in latex. And the single cementitious material that is used more than any other is Portland cement concrete. Castor oil is the single most used release agent for concrete in latex. Other cementitious materials used in latex molds are CSA cement, refractory cement, gypsum cement, and plaster.

Here are some specific tips and instructional info for using castor oil as a release agent on the inside (the cavity) of your mold. These tips are oriented toward castings of moderate size but quite a bit larger than concrete jewelry castings. Adjust the advice using common sense if you're making very small castings.
Pure castor oil alone is too viscous to be used. It will build up on the mold and cause defects such as voids and other surface defects on the casting. Castor oil is mixed with an alcohol, usually isopropyl (rubbing alcohol, 91% or higher) or denatured (which is 99% ethyl alcohol). Methyl alcohol is also sometimes used and will work just as well as the others, but methyl alcohol by itself is poisonous, so it's not a good idea to be handling it when it's necessary to mix it with castor oil.
Of denatured alcohol or isopropyl alcohol, denatured will evaporate the quickest (you have to let the alcohol evaporate from the the castor oil/alcohol before pouring your casting material into the mold). However Isopropyl alcohol is more "gentle" than denatured and I like to think it's less hard on the mold because it, too is a factor in what you put on the latex surface, and how it can affect the latex. The proportions of castor oil to alcohol can range anywhere from 1 part castor oil to 1 part alcohol up to 10 parts alcohol. A starting point of 1 to 4 might be good. If you're castings release easily from that you may want to consider decreasing the amount of castor oil because alcohol is less expensive than castor oil. If your castings have surface defects you should also decrease the proportion of castor oil. If your castings are not releasing easily then increase the amount of castor oil.
The usual method of applying the release agent to the mold surfaces is by spraying. A simple spray bottle of some product like Windex, when empty will work. Spraying is the quickest but if your mold is small brushing a very thin layer will work. If your release agent has higher amounts of castor oil you may want to brush or wipe the latex surface with a rag to spread the castor oil evenly.
Castor oil can be of use in other applications involving latex molds. One is making mother molds if your latex mold is large or very thin. In that case you will need to support the mold so its flexibility does not distort it when pouring the casting material into the mold cavity. A mother mold is made by applying plaster or resin/fiberglass to the outer surface of the latex mold while the mold has a casting in it (so its shape is true). You will want to be able to easily remove the mother mold from the outer mold surface, so, apply a few coats of the castor oil release agent to the outer surface of the mold. If you're using resin/fiberglass then use the PVA barrier coat. Read one of the latex descriptions we have for the latex mold rubber we sell to understand some of the complexities of how mother molds work and how they're made.
Yet another application for the castor oil release agent when working with latex molds is when you need to apply latex to your latex mold and you want to separate the secondary application of latex. For example, you may want to make a rigidized but still somewhat flexible mother mold that's more forgiving of slight undercuts or that can be made with fewer sections than a plaster mother mold. You would first use pure latex against the outside of the mold, then you would use a "backing" latex mixed with a latex accelerator to cure thick sections of latex and to stiffen them. Use the same application of castor oil release agent as described in the above paragraph.
Another place you might be applying latex to latex is if you want to make a positive casting of latex rubber by slush casting latex inside your latex mold. You would again apply a heavier coat of castor oil release to the inside of your latex mold (just to be absolutely sure the latex positive will release).
One other use which I have never seen mentioned is using castor oil on the object that the initial latex mold is made from. Although latex will not stick well to almost any material; it just peels right off, I have had certain occasions when it was difficult to peel the latex mold from the positive object. This has happened when making vulcanized latex molds that have been vulcanized with the original object still within the mold. That's done so that an completely true shaped vulcanized mold is produced. Vulcanizing latex makes it even stronger and long lasting, although it also makes it firmer (higher durometer) which may or may not be desired. It can be semi-vulcanized so you can choose how soft and stretchy versus how firm and stronger you can make it is available.

Castor oil itself is an interesting oil. We sell another material that's made from it, castor wax, which has its own unusual qualities among waxes.
To make the wax the usual method of increasing molecular weight of a liquid is used, hydrogenation. The wax is hard and very shiny. We sell castor wax mainly as an art material used in wax painting. One type of wax painting is encaustic which is painting with warm melted wax mixed with pigments. The other is called "cold-wax", which uses much lower quantities of wax mixed first with a medium such as odorless mineral spirits at low heat, after which pigments are added to the resultant medium.

Other uses for castor oil are concisely given by the arts database, CAMEO:
"Castor oil is a transparent, viscous liquid with a mild odor and an acrid taste. It contains ricinoleic acid (83-89%), Oleic acid, Linoleic acid, Palmitic acid, and Stearic acid. In very thin layers, castor oil takes over a month to dry and thick layers never completely dry. Castor oil has been used as a lamp oil, lubricant, paint plasticizer, soap ingredient, and as an emollient to keep leather supple in low humidity areas. Dehydrated castor oil dries to a flexible but slightly tacky film. It is nonyellowing, water-resistant, and is used in alkyd paints and varnishes."
Here are paraphrased excerpts from a well written Wikipedia article on it:
Castor oil is a vegetable oil cold-pressed from castor beans. It's used in the manufacturing of soaps, lubricants, hydraulic and brake fluids, paints, dyes, coatings, inks, cold resistant plastics, waxes and polishes, nylon, pharmaceuticals and perfumes. Castor oil is well known as a source of ricinoleic acid. It tends to be more polar than other fats. It is more expensive that other vegetable oils because of its value as a feedstock for many important secondary compounds. For example lithium grease uses a large amount of castor oil in its production. It has uses in making lubricants in other areas because unlike other vegetable oils it can be made to replace petroleum lubricants because it has good oxidative stability. It has
better low-temperature viscosity properties and high-temperature lubrication, making it useful as a lubricant in jet, diesel, and racing engines. If you've heard of the Castrol brand of engine oils they took their name from the castor oil used to produce them. If you've heard of Castrol how about "Turkey Red Oil"? It's sulfated castor oil (made by adding sulfuric acid to castor oil). It was the first synthetic detergent after ordinary soap. It is also used in formulating lubricants, softeners, and an anionic surfactant that has long been used as a dyeing aid. It's also used in textile and sugar manufacturing, as a defoaming agent in paper making, as an emulsifier, wetting agent, and in cosmetics and essential oils as an emulsifier. It is said to be the only oil that will completely disperse in water. One source reports it has a distinct and "heavy" scent. I wonder if it's related to Red "Marvel Mystery Oil"? I'm going to have to get some!