Hi, I know this is a very old post, but it helped me greatly in making my own rose petal clay, thank you for writing it!

I don't know if it matters for any sort of ritual whether the clay be used immediately or not, but I thought it might be useful to know that the clay actually keeps very well in the refrigerator !

I have kept mine for nearly a month and a half by storing it in a tightly zipped Ziploc bag with the air squeezed out, with the bag kept in an airtight container with a dampened paper towel. The whole thing goes in the fridge, and when I want some, I scoop out what I'll use into another bag, so the large container doesn't leave the fridge. I do check on the paper towel occasionally to ensure it's still damp.

I also added a little bit of clove essential oil to my own clay, to ward off mold, it seems to work well. :)