How is this different than the stuff I buy in the store?
Wood ash lye has a different chemical makeup than commercially produced lye. Lye made from wood ash is potassium hydroxide. Lye made commercially is sodium hydroxide. These two products are not interchangeable. The amount of lye you use in a recipe varies based on which product you are using.
What's the best ash to use?
The best ash to use to produce lye (sodium hydroxide) is from hardwoods like oak or maple or fruit trees like apple. Avoid using wood from pine trees or evergreens. The wood must be burned at high temperatures with lots of oxygen so that the wood is completely consumed leaving white, paper thin ash, not chunks of charcoal.
Collect enough hardwood ash to fill a waterproof non-metal bucket to within 3 or 4 inches of its top edge. This container may be as small as a five gallon plastic container or as large as a wooden barrel.
You will need two non-metals containers for your project. One bucket will hold the ash, the other container will catch the runoff. Drill a small hole near the bottom of the ash container. This hole should be small enough that it can be stopped with a non-metal object like a small cork, toothpick or dowel.
In the bottom of the ash container, place a layer of clean river gravel. On top of this, place about 4 inches of packed straw, hay or grass. Fill the remainder of the bucket with wood ash (stop 3 to 4 inches below the top) and tamp it down firmly.
Collect 5 or more gallons of soft water. Soft water is water with little or no mineral content. This water can be acquired by use of a specialized filter, or from peat or, sandstone or lava rock sources like granite. Another alternative is to distill the water you have. However, the simplest way to acquire soft water is by collecting rainwater.
Put your ash container in a secure location away from high traffic areas or places that children or animals might bump, or knock it over. The container you will use to catch the runoff can be glass or even an enamel surfaced pan. Metal containers will react to the lye which could eat holes in the container. Find a position for this catch container that is close enough to the ash bucket to prevent unnecessary splashing during drainage.
SAFETY & PRECAUTIONS
Lye may cause blindness. If swallowed it can be fatal. Potassium hydroxide (lye) is caustic and can burn anything that it touches, especially fats and oil on skin. This reaction creates salts which can cause severe chemical burns, permanent injury or scarring. Lye burns can be so severe as to cause nerve damage, so you may not feel the burn right away.
It is necessary to take safety precautions before you begin the process. Work in a well ventilated area. Have contact information for emergency and poison control on hand. Dress appropriately. Wear rubber gloves (the big yellow kind), long sleeves, have your legs covered and wear safety goggles. Keep vinegar nearby in order to neutralize any skin burns. Do NOT wash with water following contact with this substance as this will merely exacerbate the corrosive affect.
Use a broom handle or dowel to create an indentation in the packed ashes. Bring 1 gallon of your soft water to a boil. Carefully pour this into the ash bucket. The water will react with the ash by bubbling, spitting and splashing. When this action calms, slowly add another gallon of water to the ash bucket. If the level of the ashes sinks, add more ash to the bucket. Continue to add water until the ashes are covered. Place a lid over the top of the ash container.
Remove the stopper from the hole at the bottom of the ash bucket and allow the runoff to drip into your catch container. This can take a whole day.
Repeat this process on days 2 and 3 by pouring the runoff through the ashes again. This will add to the strength of your lye.
An alternative method is to add the water to the ash container while the stopper is still in place. Cover the container and allow the water to sit for about 3 days. Make sure it is in an area where it can't get spilled. After three days, remove the stopper and drain.
The resulting liquid is lye water (potassium hydroxide). To test its strength place a fresh egg (still in its shell) into the liquid. It should float on top with a nickel-sized or quarter-sized area exposed above the surface (2 cm to 2.5 cm diameter). If the egg sinks, the lye water is too weak for soap making. If the egg bobs on top of the surface, the lye is too strong and needs diluting with more rainwater. Be sure to dispose of the egg after use.
If the lye water is too weak, heat it to reduce the amount of liquid. Enamel finished pans are safe for this as long as they are never again utilized in cooking foods. Be careful when heating lye as it can be scorched. The solution is strong enough when a chicken feather touched to the heating lye starts to dissolve. Remove the lye water from the heat to cool.
Store lye water in jars with plenty of head room to allow for safety in pouring. Keep in a cool, dark place in tightly sealed containers, away from curious children.
Dispose of the old leached ashes in a hole dug away from high traffic areas. Allow this to cool thoroughly before re-filling the hole.
MAKING CRYSTALLIZED LYE -- POTASH
If you wish to dry your lye into potash crystals, place the water into a lye-safe container. Glass is a good choice for this application. Leave the container uncovered in the sun until the water evaporates. Follow the same storage precautions with potash crystals as you would the lye water.
Here's a video I found on YouTube that shows a Living History interpreter explaining how settlers used to make their own lye from ashes using an ash hopper. The sound level is low, but the information is good.