Amazing Pottery - How would I seal my Oma's ashes into the bottom of a hollow pedestal of a clay pottery piece?

How would I seal my Oma's ashes into the bottom of a hollow pedestal of a clay pottery piece?

the clay cannot be refired or it will crack. The hole that requires sealing is about the size of a coffee mug.

sorry about ur grandmother.
Go to a pottery place and make a special one from you for it. Dont tell them what your doing though.......
I've seen porous pottery sealed with wax - either paraffin or beeswax - if you can, fit another container inside the pedestal, then pour wax on top and around the edges. It's not permanent - if you want it permanent, try the same method using 2-part epoxy glue that you can buy in the hardware store.
If it was me, I'd mix up some Bondo (Automotive body filler) and (Slowly and carefully) begin filling the hole. It would take some time and several applications because you wouldn't get the whole hole in one pass. Apply some around the edge to start filling the hole. Let it cure. Sand gently. Apply more to the now smaller hole. let cure, sand gently. Apply more to the ever shrinking hole...get the picture?