Investment-'to cloth, cloak or surround (Latin root)Can withstand high burnout temps.
Made of gypsum-a white mineral, calcium sulfate, responsible for the hardening of the plaster; silica-white and colorless mineral, quartz, to cushion while expansion and contraction (this is the main material that is harmful to breath in (wear a respirator) ; cristobalite-pure silica, enables to withstand the high temps. Some investments contain fiberglass for strengthening.
Store in resealable bag to avoid being exposed to moisture--use within 6 months or less.
If you suspect it has been exposed to moisture, measure it against some investment you know is fresh. (throw out if its more than 20% heavier than the new)
Never pour investment down the drain and use rubber mixing tools that the investment will easily crack off of to be thrown out.
Mixing
When mixing, you want to get a proper ratio between powder and water, mix it evenly, make sure there are no air bubbles, and do it within a specific amount of time.
Before mixing, make sure the model is clean, renove all dry investment from flask and mixing container, check to make sure the the fit is watertight, make sure the sprue is in tact, paint the model with debubblizer-denatured alcohol can work too but a debubblizer is not neccessary.
Investment has a working time of about 9 1/2 minutes. Hardening too slow will not give the investment time to properly settle around the mold. Hardening too fast will cause the investment to separate and bubble.
Use water of consistent temps.
Mix investment in a ratio of 38-40 parts of water to every 100 parts of powder by weight. Always add powder to water and not visa versa. Mix for about 4 minutes. Consistency should be a little thinner than sour cream.
A vacuum machine can be used to shake out air bubbles. Prepare this ahead of mixing. Tape a piece of paper to the top of the flask to catch any investment that might spill out while in the vacuum. Bubbles can also be vibrated out by a massager.
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