A recipe I found on Glazy.com
Test tiles fired to ^6 in an electric kiln with a regular slow cool (cooled down 150F per hour from 1900F - 1400F).
Not very runny and a pretty cool crystal effect without any super fancy kiln cycle.
Here is a link to UMF info and charts on Glazy.com
% Frosty Crystal
40 Nepheline Syenite
17 Zinc Oxide
Mixed to Specific Gravity of 1.50
Floccing not necessary
Cobalt Carb. 1% + Rutile 2%