lime from Oyster shells

Instructions for making oyster shells into lime aka quicklime exist in Mappae Clavicula (Smith and Hawthorne 51-2). I'll include the authors note too as I think it's an interesting judgement about the resulting purity of the product.

(Smith and Hawthorne 51-2)

Lime is CaO, calcium oxide. Slaked lime is basically just lime 'slaked', or mixed, with water turning it into calcium hydroxide Ca(OH)2.

Lime was useful medievally and broadly employed for painting (Merrifield 298-300) and building houses among other things.