With the advent of Milled Crowns, the use of casting investments is slowly being reduced in the laboratory. This reduction in daily use often leads to a loss of the critical information that laboratories need to remember about these products. Let's examine what that information might be and the six reasons that it is important.

1. One piece of important information is the behavior of these specialized investment liquids when they are used with phosphate Investments. Most of these materials use a colloidal silica based investment liquid. The concentration (density) of the colloidal silica in the liquid depends upon the powder's chemical formulation.

2. All colloidal silica liquids are not freeze stable. Being Freeze Stable is the ability of the liquid to remain viable even after it has been frozen and then thawed. An example of something that is not freeze stable is milk. When frozen, milk separates into water and the remainder of the solids; calcium, fat, and etc. After it's been thawed, have you ever tried to turn it back into milk? You just cannot do it, no matter how much you shake that jug. It's the same for non-freeze stable colloidal silica liquids. They simply will not convert back into a useable solution. It is for this reason that for many years Whip Mix Corporation has suggested a “Beat the Freeze” purchase of liquids for transportation and use during the winter.

3. In the past, Whip Mix provided the liquids in the box with the powder. However, in the winter months, shipments often result in un-useable liquids upon arrival at the laboratory. We decided it would be better for the customer if we separated out the liquid and let them purchase enough in the Fall to get them through the winter, and then purchase the powder as needed.

4. Whip Mix also consolidated the liquids into three (3) major liquids; Special Liquid Concentrate (Freeze Stable), Fastfire Liquid (freeze Stable) and Special Liquid Concentrate Plus (not Freeze Stable). If you have other Whip Mix labeled liquids, please call technical support and we will help you determine the correct liquid for your powder product.

5. Whip Mix also added a color to two of the liquids for better identification; Special Liquid Concentrate is light blue, Fastfire Liquid is purple and Special Liquid Concentrate Plus is clear. The added color does not change or contribute to the performance of the liquid.

6. Laboratories will sometimes call in to tell us that their liquid has gone bad, because they are having problems with castings. Bad liquid can be separated into three categories, in addition to being frozen, then thawed;

1. The original water dilution has changed due to evaporation (open bottles). This could produce a larger casting size -- even with the same ratio.

2) Large crystals have begun to grow in the bottom of the bottle. That indicates that colloidal silica is coming out of solution.

3) The liquid is turning a brown-black color. This can be from the presence of bacteria.

If you experience any of these conditions, the liquid should be discarded and new liquid used.

Please call Technical Support if you have any other questions about your investment or liquids.

 

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About The Author

Craig A. Pickett is NBC certified in Crown & Bridge with Technologist designation. A 30 year CDT, Craig is currently Technical Support Manager for Whip Mix Corporation. In 2014, Craig was the recipient of the NADL Excellence in Education Award.