How to Best Use Prosthetic Grade Alginates in Life Casting
Today's life casting alginates evolved from dental formulations known as dental impression material. In fact, the alginate definition is referred to as impression material in dentistry. However, alginates are also widely used in the medical field for dressings and wound care and also in the food industry as a food supplement.
Alginate used in life casting and mold making is distinguished by slower setting times as compared to dental formulas. Most formulations consist of raw materials, known as sodium alginate or potassium alginate, which are refined from seaweed, specifically giant kelp. These materials are then combined with other ingredients to make a gel-like substance when mixed with water.
Because alginate-based impression material was originally designed to take molds inside the mold, its ingredients are hypoallergenic and completely skin-safe . . . the perfect material for taking molds of the human body. In fact, it is so gentle on the skin it is used to take life cast impressions of even the youngest child.
Alginate impression formulas are known as waste molds as they can usually only be used for one . . . perhaps two castings. That is because being composed primarily of water, the mold shrinks over time as the water evaporates. Thus, it needs to be cast into its mold within 3-hours for best results. This can be delayed by placing the mold in an air tight bag with a wet rag or placing the mold in a refrigerator to eliminate evaporation and to extend its useful life.
Dental impression material was discovered by life casting artist’s because it set rapidly, to a soft rubber-like consistency eliminated a model’s discomfort posing for lengthy periods. Fast-setting meant that the molding procedure could be done rapidly without exhausting the model. The more comfortable the model, the more perfect the mold.
Over time, alginate manufacturers modified its impression materials set-times from the usual 2-minutes to as much as 8-minutes. This gave the life casting artist more time to complete larger molds. So that now an artist can obtain alginate impression materials for life casting, ranging from two to eight minutes of cure-time.
A two-minute set time is best used with children and infants for hand and feet castings. Whereas, an eight-minute set time is based used for head and torso molds.
There a number of alginate characteristics a user should be familiar with to perfect their molds. Most manufactures specify set-time based on a specific water temperature of 80-90-degreesf F. (26-32 C). The colder water the slower the set time (and also the more uncomfortable the model). The warmer the water the faster the set time.
Another characteristic that effects set-time is the thickness of the mix. The thicker the mix, the faster the set time, and visa versa, the thinner the mix the slower the set time. This phenomenon is an important consideration as the artist will want a thinner mix when using alginate in a container, say to cast a hand. But want a thicker alginate mix when creating a mold of a vertical surface such as a torso or a face. The life caster must account for the different set times when using thin or thicker viscosity.
A thicker mixture has a harder time allowing air bubbles to come to the surface. The artist must remember to watch for such anomalies when using a thicker mix. The manufacturer will have its recommendations on the package; however, the experienced artist knows that they can best achieve the results they want by initially experimenting with, and testing different thicknesses and temperatures before attempting mold making.
One of the most important considerations in mixing alginate from any manufacture is the quality of the water that you use. All dentists are taught to use distilled water when mixing dental impression material. That is because alginate impression formulas contain a precise amount of calcium salts to regulate setting time. Excess calcium will cause unwanted effects and can render the alginate mix unusable, thus spoiling a life casting session.
If hard water is used, a smooth mix is unattainable. The mix will look like cottage cheese. Filtered water is NOT soft water. So, when in doubt about water quality, a gallon of soft water from the super market is the safe choice. It will save an artist from a failed mold making sessions.
When casting into an alginate, almost any water-based casting material can be poured into the mold to make a cast, even hot wax. Resin must be avoided though as resin will foam up on contact with moisture. Using a casting material that generates excessive heat, can turn the water in the mold to steam which could damage both the mold and the cast.
EnvironMolds produces two classes of impression materials.
The first group is a silica-free formula which is both environmentally and user friendly. This family of alginates has a softer set, which is ideal for casting babies and small children as it is very gentle on the model. The silica-free formula provides a much greater coverage as its mix ratio is 1-part powder to 7-parts water, (compared to traditional formulas using 1-part powder to 3-parts water) making it one of the most economical alginate formulas on the market when valued by volume produced.
The second class of alginates is a traditional formula which provides for a firmer set due to its clay fillers. But the traditional formula has the classic mix ratio of 1-part powder to 3-parts. Thus, it has a lesser coverage by pound, then the silica-free family. But its higher strength makes it the better choice for larger molds as they are less apt to tear.
EnvironMolds also produces its FiberGel brand which contains fiber in the formula to improve tear strength and to hold moisture which significantly delays shrinkage. This is an excellent alginate formula for larger molds and life castings.
Whatever alginate is chosen, with these few usage suggestions, a life casting artist should be able to quickly master life casting mold making technique with a just a bit of practice.