FREQUENTLY ASKED QUESTIONS
The following questions are frequently asked our Staff. if you have any additional questions not posed here, please don't hesitate to contact us.
MOLD MAKING & CASTING
How can I preserve a piece of sculpture that I have modeled in Plastilina?
When a piece has been completed, oftentimes reproductions are desired as gifts, for display, even for sale. To make the reproduction, a mold and cast of the model must be made in one of a variety of casting mediums, such as plaster, bronze, or bonded bronze. A mold is the negative or hollow cavity produced around a sculpted piece for use in creating multiples of that piece. A cast is the positive or reproduction of the original piece of sculpture created by pouring casting material into a pre-formed mold.
What materials are needed to make a mold and cast?
Some of the most popular materials used for mold making include: plaster, latex rubber, paste maker, moulage, gelatin, white rubber and polymer or chemically activated multiple part mold rubbers. Popular casting materials include: plaster (Gypsum), resin, metal (bronze, aluminum, lead, silver and gold), and casting rubber.
Can latex rubber be poured and set solid?
No. Latex must be applied one coat at a time and air dried before adding another coat. If poured, the latex will seal on the outer layers, preventing the inner latex from setting. Only a material with a chemically curing agent can be poured solid, such as white rubber, Tuffy, and silicone.
How long will a latex mold last?
Up to 20 years, if stored properly. You can boil the cured rubber to vulcanize it: submerging it in boiling water for 20 minutes will give the rubber longer life.
Can latex be colored?
Yes. A water soluble pigment, such as clothing dye, can be mixed with the rubber while it is still liquid.
Can you cast latex?
here are two types of latex rubber. The most commonly referred to latex rubber is the mold rubber used to make a negative mold. The negative mold is encased with a plaster mother mold or retaining mold so the rubber will hold its shape during casting. Casting rubber is the latex rubber used to make a positive rubber cast or mask. The casting rubber is poured into a plaster mold (and only a plaster mold); after setting for a few hours the rubber forms a thin layer on the mold’s surface - the excess liquid rubber is removed. The resulting rubber is left to set and cure and when removed from the mold becomes a positive cast piece. Note: Mold rubber can only be used to make a negative mold. Casting rubber can only be used to make a positive cast from a plaster mold. An easy way to remember this is: mold rubber for the negative mold; casting rubber for the positive cast.
How long will latex keep in its container?
If the container is kept airtight the latex will last for years. When exposed to light the material will take on a pink hue but this does not effect its workability.
How do you clean up after using latex?
Latex is an ammonia- and water-base natural rubber and tools and brushes can be cleaned with warm water. Keep the brush in a water solution while working and then dry with a cloth when finished. Set rubber can be peeled from tools and other surfaces when dry.
Can latex be applied over dried latex?
Yes. Although this is not recommended if the material has been cured for more than 24 hours, since layering will occur. Apply the next coat of latex when the previous coat is dry. Trouble occurs after it cures for 24 hours - additional coats of latex won’t adhere properly.
If the latex thickens how can it be thinned?
Latex can thinned with either water or household ammonia. Do not thin the latex too much since it will weaken the strength of the material.
How do I stop pooling?
Pooling is caused by allowing the rubber to build up; a film will then cover the outer layers before the inner material has set. This usually occurs in cavities or at joints. Take a pin, or sharp pointed object, and puncture the semi- sealed area and let dry. Sometimes a Q-tip will work well.
I get soft spots. How can that be avoided?
Soft spots occur where the rubber has set before the inner material is dry. The interior rubber remains liquid or semi-liquid and leaves a blemish on the positive cast. This can be avoided by applying the latex in thinner coats and allowing each coat to dry thoroughly before applying another one. Once the mold is made this defect is very difficult to correct, if at all. Sorry.
The mold takes on the color of the casting material. Can this be avoided?
The rubber will pick up the color of the casting material especially if it is black or dark brown. Casting lighter materials will alleviate this somewhat. Make light casts first, then the darker ones. If a series is to be made of different colors, we recommend separate molds for each color be made from the master cast.
The latex has a pink tint. Is this a problem?
No. When latex has been exposed to sunlight, even in its container, a pink hue will result. This will not affect the integrity of the latex.
Can latex be applied directly to the human body?
No. This will block oxygen from the pores and cause damage to the epidermal tissue.
Who is best trained to cast in resin and bronze?
When casting with resin, plastics such as fiber glass, or even soft metals, special types of rubber molds and releases are required. Each manufacturer will recommend the proper releasing agent for a specific rubber depending on the material being cast into that rubber. To cast in resin and bronze is an advanced technique and professional mold makers and casters should be retained for these projects. Bronze casting should definitely be left to the professionals.
Is there a superior patina kit for the amateur and/or professional sculptor?
Yes, Ron Young, highly regarded throughout the world for his knowledge and use of patinas, has developed a patina kit for gypsum and fired ceramics that is by far the best we have ever seen.
