How to make crayons using soil as a pigment
by Dr. Dirt (Clay Robinson, PhD, CPSS, PG), December 7, 2013
See the youtube video: http://www.youtube.com/watch?v=mvebCxFxFCw&feature=c4-overview&list=UUm0_6Kd2ys5K6q4w4bhyKsw
Select colorful soils
Watch road cuts as you travel (take some sealable plastic bags).
When you see something colorful, stop and collect a sample.
When someone digs a hole, collect samples at different depths.
Use friends, students, club members to enhance your collection, suggesting they collect soils when on trips.
Dry the soils.
Leave the bags open, and stir the soil occasionally, or
Spread the soil on a baking sheet covered with aluminum foil or wax paper.
The time required for the soil to dry depends upon how much water was in it, and what the ambient (weather or room) conditions are (temperature, humidity).
Oven drying is not necessary.
Crush/grind the soils (Remove any rocks first). Options:
This is best done outside.
Use a hammer to crush the aggregates.
Use a mortar and pestle.
Use a coffee grinder or blender. (Ask permission.)
Sieve the soils.
This is best done outside.
If standard screens are available (in a lab), only particles finer than about 0.5 mm will work without abrading the paper; coarse sands do not work.
Window screening may be used. Place a container under the screen. Pour the crushed/ground soil on screen and shake the screen.
Womens’ hosiery may be used. Place the soil in a cup. Stretch the hosiery over cup, and shake the cup over a container to catch the soil that passes through the hosiery.
Prepare the indoor workspace.
Place newspapers or other disposable/recyclable materials on the workspace to catch spilled soil or wax.
Prepare the wax.
Use paraffin such as Gulf Wax.
Shave paraffin into a container, such as a pint or half liter can or glass jar.
Put water into a pot and heat to just below boiling.
Place the container of paraffin into the pot.
When the paraffin melts, it is ready.
Prepare the mold. Options:
Hard plastic, pointed-end centrifuge tubes
Ice trays that form cylinders (rather than cubes), lined with parchment paper or aluminum foil
Shaped rubber/plastic molds (animal, cartoon characters, or others of your choice)
Mix and pour.
Mix about equal portions of soil and melted paraffin.
45-ml (1.5 oz) small plastic containers (Glad, Ziplock, or other brand) work well
Chopsticks, craft sticks, or similar item to stir the mixture.
Pour about 15-ml (1 tablespoon) of melted paraffin into one container.
Pour an equal volume of soil into another container.
Slowly add the soil to the melted paraffin and stir. (There is a bit of art in this step. Clay soils respond differently than sandy soils. Practice will provide the experience to know the best ratio. The mixture will thicken. With too little soil, the soil will settle to the bottom. With too little paraffin, the crayons will not stick together. More sand is required compared to clay or other fine-textured soils.)
Continue stirring the mixture while pouring it into the mold.
An ice bath can be used with hard-plastic containers.
Ice trays or molds can be placed in the freezer or refrigerator.
Molds can be left on the counter or table overnight.
Remove and enjoy!
Some soils have beautiful color, but do not make good crayons, as the color does not transfer to the paper well.
Experiment to get the right paraffin to soil ratio.
Make one or two crayons with each soil to observe which will make good crayons.
Another soil crayon recipe and procedure can be found here: http://www.nrcs.usda.gov/wps/portal/nrcs/detail/ct/people/teachers/?cid=nrcs142p2_011212