Casting Tracks, Any new developments in technology? Options

[Sasquatch]

I've just finished searching through 17 pages of search results and unless my search terms were off, as far as I can see the most recent threads on how to cast a track are 4-5 years old.

Five years ago, the consensus was that platster was an inferior casting medium, and that a product called Ultracal 30 was recommended. Have there been improvements in technology, casting medium, or casting techniques since that time?

This post has been edited by Sasquatch: Dec 14 2007, 10:41 AM

[Hominid,WA]

As far as I'm aware, casting medium and technology have remained consistent over the course of 5 years. Splash casting has received some attention. Regarding casting technique, there has been analysis done on casting artifacts, how they might occur and how to read them. I'm not the expert on casting by any means, but a few on this forum have extensive experience concerning this.

This post has been edited by Hominid,WA: Dec 14 2007, 02:04 PM

[jasonch1112]

The only thing I have really heard it that you need to avoid anything that tends to create bubbles so that they aren't mistaken as pores. And it has to be able to keep it's form well. I personally think that casting have become more of a stutus symbol than evidence gathering. It almost seems as a 'look at what I found' thing now.

[Flashman]

Anyone still working on the molten sulphur technique for casting in snow? Was reading a news story the other day about how the CSI types use it.

[xpert4u]

As far as casting in dirt, I have been prespraying with regular hairspray before casing with dental stone. In snow I use a spray casting wax and then dental stone.

[Melissa]

I know many use fixatives like Hairspray - but I have never used it, and in my own casting have been able to cast my own dermal ridges in everything from soil to fine pumice.

Oh, and thats using both splash casting and pouring straight into the impression.

[wolftrax]

I don't make any claims to be an expert. Regular plaster of paris will break easily, Ultracal 30 is a lot stronger. Using a fixative has been shown to prevent casting artifacts (that resemble dermal ridges) in pumice and fine volcanic ash. The best thing is just to experiment.

[xpert4u]

I know many use fixatives like Hairspray - but I have never used it, and in my own casting have been able to cast my own dermal ridges in everything from soil to fine pumice.

Oh, and thats using both splash casting and pouring straight into the impression.

Only been to Texas one time in the Dalas area, but where to you find pumice in Texas? And if it was pumice was it wet and compacted or dry? If it was dry, I would bet the dermals were artifacts.
Thats why I use the hairspray on any ground that has a loose cover. JMHO

[Melissa]

Only been to Texas one time in the Dalas area, but where to you find pumice in Texas? And if it was pumice was it wet and compacted or dry? If it was dry, I would bet the dermals were artifacts.
Thats why I use the hairspray on any ground that has a loose cover. JMHO

The pumice was ordered from a store in Seattle (Long story)

There are some very dry soil types in Texas (West Texas) I still want to try out.

Suffice it to say, no they were not artifacts - they were my own dermal ridges. I have yet to create artifacts in any substrate other than pumice (at least artifacts that look like dermal ridges). But, Im trying.

But, I have moved recently, work has been horribly busy and have not had the time to put into my final article - but I am getting back to it.

I have tried out various fixatives - and have yet to find one that I think is worth the risk in using it. Especially when I am getting such good detail in my finished casts without it.

*Shrug* I know many law enforcement agencies use these things - and many researchers, I just have not found the benefit myself.

This post has been edited by Melissa: Jan 31 2008, 08:51 AM

[xpert4u]

The pumice was ordered from a store in Seattle (Long story)

There are some very dry soil types in Texas (West Texas) I still want to try out.

Suffice it to say, no they were not artifacts - they were my own dermal ridges. I have yet to create artifacts in any substrate other than pumice (at least artifacts that look like dermal ridges). But, Im trying.

But, I have moved recently, work has been horribly busy and have not had the time to put into my final article - but I am getting back to it.

I have tried out various fixatives - and have yet to find one that I think is worth the risk in using it. Especially when I am getting such good detail in my finished casts without it.

*Shrug* I know many law enforcement agencies use these things - and many researchers, I just have not found the benefit myself.

I only use the hairspray, 1. when its called for in really loose soil & 2. Because I'm cheap..
I think it prevents particles from falling inward when pouring into the print.

[Bill]

Funny I just put up a thread on foot casts in the general discusion area, and then found this thread.

Can answer some of the questions, having used Ultracal 30 for many years.

Plaster is rated by crush strength (hardness, essentially) and Plaster of Paris or Pottery Plaster run about 1500 pounds, crush strength, as i recall. UltraCal 30 runs more in the 3500 to 5000 pounds range, much harder. But dental stones run up to 12,000 pounds (pricy stuff, but gets the job done.

UlrtaCal 30 would suffice very nicely. The 30 means 30 minutes to set, as opposed to UltraCal 60, with a slower setting (60 minutes). But setting time isn't surface hardness time. The actual surface in contact with your ground may not harden for 2 to 3 hours, as far as being hard enough to pull and clean the ground away.

There is a material I once used, I believe called Hydrostone, great compressive strength (maybe 11,000 ppounds, close to the best dental stones) and incredibly low viscosity (meaning very fluid, better to release air bubbles and not leave any trapped on the surface of the plaster touching the ground. In fact, it's so fluid, you can only pour it into a bowl-like impression or something with a wall around it, because it doesn't thicken enough to lay up or otherwise build up on a angled or vertical surface.

But the hydrostone would be great for casting footprint impressions. Not to expensive, real hard, wonderfully fluid to avoid air bubbles.

On the hairspray thing, you can also use Krylon Crystel Clear spray. Works great so putting a super thin sealing coat over the earthen material of the impresion, and makes cleaning the cast easier. Just make sure you give the cast 2-4 hours to really cure before removing.

If you pull a cast too soon, the surface can be so weak and moist that it actually forms artifacts in the surface which could be mistaken for detail in the footprint.

Also, plaster has a "consistancy", it's recommended ratio of powder to water, for ideal strength and setting. More water (which thins the plaster mix) will generally lower the consistancy, weakening the final cast. If you start with a thin mix to get a better pour without air bubbles, then sprinkle more plaster powder into the wet plaster to thicken it, well before it sets, to reaise it's consistancy back up.

Bill

[Drew]

Bill-

As a costume person, isn't Latex used to make many of the masks and things that Hollywood uses?
It seems to give a detailed impression, why wouldn't liquid latex be used for casting foot prints? Why plaster?

[Bill]

Drew:

Latex is cured or hardened by evaporation of the water in it. Plaster is a chemical cure (mixing with water changes it chemically), and that chemical reaction will harden the plaster regardles of thickness.

So if you pour a footprint full of latex, it will harden on the top surface in contact with the air (skinning the top) and some water may be drawn out by the earthen substrate below, so you may get a thin hardened surface against the ground, but the entire center volume will still be liquid, and the whole thing falls apart when you try to remove it.

Plus, when the latex loses the water and hardens, it shrinks, maybe 10-15% of it's overall dimensions. Plaster has a far greater dimensional integrity when set, nearlty the exact size when poured as a liquid.

So latex is never used for casting large, solid objects.

Bill

[Bill]

Following up on my earlier mention about hydrostone (since it's been years since I used it and wasn't sure it was still around), I googled it and came up with this nice link to the product plus other plaster materials and books.

http://www.plastermaster.com/usg/

The usg is for United States Gypsum company, which makes the hydrostone, as well as Ultracal 30.



Bill