February 5, 2016

Dermal Ridges and Casting Artifacts Part II


In the first installment of these tests, I used my own foot and Onion Mountain Soil to see if dermal ridges can be captured when the medium capturing the dermals is a soil or substrate. Answer to that question, yes you can capture dermal ridges and flexion creases. The question is still out there however, how do we prevent "artifacts" in casting? In this article will attempt to address some of these questions.

For this round of tests I used soil that had been sifted 5 times to remove as much organic material as possible, and although the soil was reused, it was re-sifted after every experiment.

It has been discussed in order for artifacts to happen, one would need to be casting in a substrate that is fine and very dry, because only these dry, fine soils will produce the needed "wicking" effect. Wicking, some may be asking "what is "wicking"? Simply put, wicking is the water being pulled from the casting agent by the soil - think of the soil as a sponge, sucking the water out of the cast. That is "wicking". Will we have the same "wicking" effect if we cast in this soil from Onion Mountain? Answer, yes it will. The soil from Onion Mountain pulls the water from the casting agent while the cast is setting very nicely.


I was confused as to how these artifacts happen, as I was not getting the desired results. I had used soil and water temperature to this point from 70 degrees up to 100, and nothing, other than what could be mistaken for flexion creases (which I know are the pour lines). I thought, well maybe its the casting agent itself? So, I decided to call I was able to have a telephone conversation with a gentleman who is an expert in casting agents and has worked with them for more than 25 years, he has also (and may continue) worked with the FBI to help them understand how to properly use casting agents in the field, during the course of their investigations.

Here is a link to the website, and if you scroll down the page you will find a thumbnail picture with the title "Plaster Mixing Procedures, USG Plasters and HYDROCAL® Brand Gypsum Cements IG503"

First he assured me, "if you can see what your trying to cast in the soil, you will cast it, if you mix the casting agent properly" (mixing of the casting agent properly was a point he drove home over and over). The water temperature should always be right around the same temperature as the air ( plus or minus 5 degrees) I asked him if organic material or any minerals play a role in the casting process or could various soils rich in specific minerals cause "artifacts" to happen. He responded by saying "No". "Minerals and organic materials will not affect the casting agents ability to retain details or cause details that look like dermal ridges when there are none, as long as your mixing properly". He said the options range from mixing too thick or too thin, or extremes in temperatures. Notice I said "extremes". Here is an example of what he discusses, with the only difference being the amount of casting agent and water.

Cast 1: 1 Cup Water
2 Cups Plaster of Paris
This mix is per the Manufacturers specifications

Cast 2: 1 1/4 Cup Water
2 Cups Plaster of Paris

Cast 3: 1 Cup Water
2 1/4 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. The first cast only shows the disturbed soil in the center of the cast (this does correspond to the area where I poured the casting agent). Cast #2 you begin to see fine pour lines toward the bottom of the cast, which show the casting agent pushing out from the center of the cast. Cast #3, you can clearly see the same effect, only more dramatic. So, what was the reason? Changes in mixing. Notice I only increased and decreased the Plaster of Paris and water by 1/4 cup, but that was enough to show changes. Personally I found this remarkable, who would think adding just a little more plaster of paris or water would create such a change in the finished cast.

After creating these 3 casts I wondered about what the gentleman from said about "extremes". I was getting close to creating "artifacts" but this goal was still out of reach. So, I decided to try the next experiment.

Cast 4: Water 105 degrees
Soil baked in oven to 105 degrees
2 1/2 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. So, even with the temperature extreme introduced with cast #4, we still do not see dermal ridge artifacts. I then wondered if I had misunderstood the casting expert - maybe it was a matter of Opposite extremes?

Cast 5: Water 105 degrees
Soil Temperature 50 degrees

Clearly this is not the case either.

So, what causes "artifacts". Is it Temperature, and how you mix your casting agent? Yes, but temperature is obviously not the only thing that will cause "artifacts". But, it is clear that if one mixes the casting agent properly and the water temperature is within 5 degrees of your current air temperature, you should only be casting what you can see in the soil. Cast #4 clearly shows what will happen if extremes are introduced into your mixing and temperatures.


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