Q&A for How to Make Ash Soap

Different oils will need differing amounts of lye to saponify. For example, olive oil will need a very different amount than lard or tallow. Use an online saponification calculator to correctly calculate how much of each to use.

Soap doesn’t need preservatives; it should be cured for 4 - 6 weeks, which helps the water evaporate and makes the bar harder.

The amount of sugar in the batter causes heat. The more heat, the darker the color can be. The age of the soap is can also change the color.

Yes, you can.

Same as of other soaps (fatty acid salts). It's alkaline, so it may be irritant to sensitive skin. In hard water, it doesn't wash well and it turns into scum. Quality also depends on the ash; if the wood was chemically treated (anti-fungal agent, polish, etc.), it could contaminate the soap.