April 8, 2007

Dermal Ridges and Casting Artifacts - Does Temperature Really Matter?

By Melissa Hovey

As detailed in numerous articles and discussions available on the web, several researchers were able to produce false dermal ridges, called casting artifacts, using various casting materials and volcanic ash. While this article does not address the issues of such experiments on the reliability of the Onion Mountain casts, it does address the need to identify how and why casting artifacts occur.

For this round of tests, soil that had been sifted five times to remove as much organic material as possible was used. Although the soil was reused due to multiple experiments, it was re-sifted prior to use.

It has been previously hypothesized by researchers that “wicking,” a process by which water is pulled from the casting agent by very fine dry soil, is the cause of false dermals. The soil from Onion Mountain indeed is fine and dry, but previous tests (as discussed in Article One) did not produce any casting artifacts.

Since wicking, at least in these experiments, did not produce casting artifacts, water temperatures, ranging from 70 to 100 degrees, were tested. These tests also did not produce any casting artifact.

Next, experiments with the casting agent were undertaken. After speaking with an expert with, who has more than 25 years experience and has worked with the FBI to help them understand how to properly use casting agents in the field, several points were made.

1. As long as you are mixing your casting agent properly, what you can see in the track should show up in your finished cast. The water temperature should always be right around the same temperature as the air (plus or minus 5 degrees).

2. Organic material and/or minerals do not play a role in the casting process, nor can various soils rich in specific minerals cause “artifacts” to happen. Minerals and organic material will not affect the casting agent's ability to retain details or cause details that look like dermal ridges, where there are none, as long as the casting agent is mixed properly.

3. Extremes in temperatures and mixing your agent too thick or thin will affect your cast.

Here is an example, with the only difference being the amount of casting agent and water.

Cast 1: 1 cup water and 2 cups Plaster of Paris. This mix is per the manufacturers specifications.

Cast 2: 1 ¼ cup water and 2 cups Plaster of Paris

Cast 3: 1 cup water and 2 ¼ cup Plaster of Paris

All water in these 3 experiments was room temperature, 76 degrees, humidity 25%. This water was not heated.

Notice the gradual change in the cast features. Cast #1 - the disturbed soil in the center of the cast corresponds to the area where the casting agent was poured. Cast #2 - fine pour lines can be seen toward the bottom of the cast, which shows the casting agent pushing out from the center of the cast. Cast #3 – the same affect as Cast #2, only more dramatic.

Although the only change between each cast was ¼ of a cup of either water or Plaster of Paris, the change is fairly remarkable. However, false dermals still were not produced.

The next set of experiments took additional “extremes” into consideration, this time temperature.

Cast 4: Water 105 degrees; soil baked in oven to 105 degrees prior to pouring; 2 ¼ cup Plaster of Paris; 1 cup water; air temperature 76%, with 25% humidity

Cast #4 shows the very same pour lines in the substrate, again only more dramatic. Even with the temperature extreme introduced with Cast #4, false dermals do not appear. The next set of experiments deal with opposite extremes.

Cast 5: Water 105 degrees; soil temperature 50 degrees; 2 ¼ cup Plaster of Paris; 1 cup water; air temperature 76%, with 25% humidity

False dermals do not appear in Cast #5 either.


Although this paper set out to determine the cause of casting artifacts or false dermals, none of the experiments resulted in producing them. However, it should be noted that extremes in water temperature and improperly mixed casting agent will result in undesired results (i.e., the inability to cast what you intend too).

End notes: “Plaster Mixing Procedures, USG Plasters and HYDROCAL® Brand Gypsum Cements IG503”

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  • At 10:37 AM, Anonymous Anonymous said…

    hey melissa great new article very informative. bill


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