◆ PARALLAX

I have been doing this eight years and I see the same mistakes over and over. People show up with plaster of Paris in a Ziploc, pour it into a print after rain, and act surprised when they get mush with no detail. This deserves serious method.

First: dental stone, not plaster of Paris. Plaster is for walls. Dental stone is harder, finer grain, and it holds texture that plaster simply will not. Second: the mix ratio. Three parts stone to one part water BY WEIGHT, not volume. A scale costs twelve dollars. Stir two minutes, no bubbles, slake thirty seconds, stir again. This is not fast.

Third, and critical: photograph the print BEFORE you cast it. Scale or ruler in frame, good light, straight down and from an angle. If the cast fails you still have documentation.

Wet ground: you are competing with water in the soil. If it is dripping, wait. If damp, a light mist of fixative first, then build a dam and pour SLOWLY. Dry ground: the opposite problem -- loose soil crumbles in. Mist it very lightly, let it set two or three minutes, then pour. Once poured, do not touch it. I know you want to. Don't. Four hours minimum in cool weather, longer in heat.

Excellent post. I have been using plaster for two years and getting mediocre results. I did not know dental stone was that different. Where do you source it? Is it expensive?

Best casting primer I have seen posted anywhere. The photograph-before-casting rule is what separates real documentation from show-and-tell. I shoot everything in triplicate now: colour, grayscale, and raking light. The cast is the backup.

One question on the ratio -- do you have a volume equivalent for field work when you don't have a gram scale? I want to know what I can do with a measuring cup in a pinch.

I have a question about the dermal-ridge claim. I have seen casts that show very clear ridge patterns -- the detail looks almost identical to human fingerprints in some examples. Are you saying those are artifacts? I ask because I have been a skeptic for years, and if the ridge thing is real it actually strengthens the case for an unknown primate rather than misidentification.

trailcam_Tony: for field work I carry a small postal scale, twelve dollars. If you must do volume, roughly 8 ounces water to 24 ounces stone, or learn the feel -- pancake batter is about right.

Cascade_Cat: I am not saying ridge detail is always an artifact. I am saying be very careful claiming what you are seeing. The finest detail in a cast reflects the finest detail of the SOIL IMPRESSION, not necessarily the foot. I have seen ridge patterns that could be real skin, and I have seen desiccation cracks -- soil drying at the print edge -- that mimic ridges exactly. The honest answer is I have never been able to definitively separate them, and anyone who claims certainty is either lying or working from far more data than I have. Document it, photograph it in detail, acknowledge the uncertainty.

Good thread. I work Midwest canine and feline tracks -- much smaller scale, same principle. Question on the fixative on wet ground: does it obscure fine detail, or does it set the surface well enough that you lose nothing? I have had moisture problems in spring mud -- casts come out soft and crumbly even after a day.

dogman_Dewey: light fixative does not obscure detail -- one quick pass, dries in a minute, it just seals the surface so the soil does not slump as the stone cures. You gain detail.

For your spring mud: I suspect you are mixing too WET. Wet ground means a thicker mix, not thinner -- the soil is already adding water. Drop your water ratio slightly and extend cure time to eight to twelve hours in cold mud. And let the cast air-cure another day before you wrap it; do not seal it in plastic immediately.

I found dental stone at a dental supply place. They wanted $45 for five pounds. Is that normal? Plaster is $8 for ten pounds. I want to do it right but the cost difference is hard to justify on a budget.