Q: I’m trying to make an ecological indigo vat for dyeing yarn blue and the recipe calls for pickling lime. What is the difference between garden lime and pickling lime?

A: They are two different chemicals. Garden lime is calcium carbonate but pickling lime is calcium hydroxide. Calcium hydroxide is much more alkaline than garden lime. You can’t substitute garden lime for pickling lime because you need a high pH to dissolve raw indigo and get it to infuse your threads. Other alkaline materials, such as sodium hydroxide (lye), could be used to make your vat alkaline but sodium hydroxide is quite caustic. A little bit goes a long way!