You can also do it in a pan on the stove top. Basically just heat up the baking soda over medium-ish heat. Once it gets hot enough, it’ll “bubble” as the carbon dioxide and water is driven off as gas. Once it stops “bubbling”, it’s done. It’s a bit faster than the oven method, but it’s more active since you have to stir it regularly.
You can also weigh the powder before and after heating it to see if it’s fully converted* to washing soda. The resulting washing soda should weigh about 1/3 less than the starting amount of baking soda.
You can also do it in a pan on the stove top. Basically just heat up the baking soda over medium-ish heat. Once it gets hot enough, it’ll “bubble” as the carbon dioxide and water is driven off as gas. Once it stops “bubbling”, it’s done. It’s a bit faster than the oven method, but it’s more active since you have to stir it regularly.
You can also weigh the powder before and after heating it to see if it’s fully converted* to washing soda. The resulting washing soda should weigh about 1/3 less than the starting amount of baking soda.