Coloring Chert, Flint & Other Porous Stones

Below are two methods that greatly influence the overall shade and hue of a finished knapped point or blade. If you would like to give some character to a piece aside from the natural color, you may find the methods that we use for our own gallery grade finished weaponry useful for your own projects. To view finished points and blades available for purchase, please visit our Points and Blades product category. To learn how to make your own knapped works of art, you may be interested in one of our all inclusive flint knapping kits found in the GoKnapping Kits category.

Disclaimer: The author of this article and GoKnapping shall not be liable for any injury, loss or damage, direct or consequential, arising out of the use or inability to use the information on this page.

Sugar Saturation Method

This process basically saturates a finished knapped blade with a carbohydrate solution via micro pores in the surface of the stone. After saturation, the blade is heated and this removes water from the carbohydrate molecule, leaving insoluble carbon in the pore spaces. Typically the outside of the stone is darkest, with color penetrating a millimeter or two into the surface. This process is usually most effective on porous cherts, and not useful at all on dense igneous material like obsidian and dacite. It is best not to chip after applying this technique.

The first step is to mix sugar of any type with water, creating a thin syrup . Make sure all sugar is completely dissolved in the solution. Ratio of water to sugar can vary and should be experimented with depending on the stone type being colored. A 1:5 sugar to water ratio is probably a safe place to start. Too thin is better than too thick as you will have to wipe these off very well after they have been saturated.

Soak points overnight in the solution. Some stone types will get translucent when they have soaked enough. The longer the blade soaks, the more likely it will be fully saturated.

After the blade is saturated, you must prepare it to be heated in an oven. To do this, the point or blade must be dried thoroughly by hand, very quickly after removing from the sugar solution. If this is not done quickly enough, the syrup will become sticky and dry on the surface of the blade (creating unwanted sheen on surface after heating). Use a clean paper towel for every point or blade as you have to dry them well and quickly. Rub the piece hard with the paper towel, getting in every nook and cranny.

After properly drying the point, dust it using dry dirt (already have some fine dry dirt prepared). This will adhere to any parts of the blade that you could not dry off well enough. Any solution left on surface will make a black crust form over that spot and it is not natural looking.

Place the dusted piece on/in a bed of dry dirt in a baking pan. Place pan in oven and heat at approx 500 degrees Fahrenheit for an hour or two. Turn oven off and allow everything to completely cool. Do not pull your blades out hot, as they might snap from cooling too quickly.

You will get variations between chocolate brown and tan, depending on the material if this is done correctly. Results vary greatly depending on variations in stone and application of the methodology. Get comfortable with any coloring process before using it on the finest of your points.

Iron Nitrate Saturation Method

This method uses Iron Nitrate 9-Hydrate crystal. This chemical is a somewhat common but expensive oxidizer that requires special shipping considerations if bought online. The crystal is used for creating a natural looking iron stain (a reddish/brown color). For this method, you will need a pair of rubber gloves to protect your skin from contamination. Same as with the sugar method, these steps should only be performed on finished knapped blades and points. It is best not to chip after applying this technique.

The general idea is to create a thick amber colored solution with the Iron Nitrate crystal and water, then apply it to your piece so that it can be soaked into the pores of the stone similar to the sugar method. Once the iron crystal solution penetrates the pores of the stone, then you will use heat to turn the Iron Nitrate solution into Iron oxide. The byproduct of heating an iron nitrate saturated stone blade is nitrous oxide. Though reportedly non toxic when pure, this can be very nasty smelling and not suitable for an in-home kitchen oven. You may want to use a toaster style oven outside for this method.

To create your solution you will mix two or three teaspoons of powdered iron nitrate crystal with a few teaspoons of water. Stir to dissolve as much as possible. You want the solution to be thick, not runny. The active agent in the solution is expensive, so be sure to save the excess for future projects.

Now you will need to add some dry, dark (black or dark brown) dirt. Dirt out of the yard should work just fine. Go ahead and get a few handfuls so you will have plenty to work with. If your dirt isn’t dry you can bake it in the oven for fifteen minutes to get any water out (beware: baking dirt smells bad!). Mix about a teaspoon of dirt into the Iron Nitrate solution. Your solution should have a thick muddy consistency.

Take your piece and rub the solution all over the surface and into any cavities, flake scars, and grooves (wear rubber gloves for this). Be sure to fully coat the entire surface of the piece, otherwise your coloring will not look natural. Let the solution set for a few minutes. Wipe the solution off with a dish towel or other cloth material after it has set for 2-3 minutes. It is very important to not let the solution dry on your stone. The more solution you wipe off after it sets, the more natural the final stain will look.

Now you will need to heat your piece to enhance the stain. Dust all of your points with your prepared dirt, and rub the dirt in with your fingers to get it into the grooves just like you did with the solution. Place the dusted piece in/on a bed of dry dirt in a baking pan. Place the pan in the oven and bake at approx 500 degrees Fahrenheit for an hour or two. Let your piece cool completely before handling. Once it is cooled, lightly wipe off any excess dirt. Results will vary.