You may size the blue topaz ring by taking some tissue paper and
wrapping the top of the ring with it then dipping in water. This
will keep the stones cool. Just make sure to size quickly so as
not to dry out the tissue. Synthetic corundum can very easily
take heat without insulation. Just remember not to quench and
don’t breath on the stone. You may also use a small metal
container and fill it with water and submerce your stones that
way. I find it a combersome method.