Give the shelf two or three thin coats of glass separator, changing the direction of the brush stroke each time. Apply the separator with a haik brush. After the separator has dried and the shelf is cool, you can smoothen the separator by rubbing your palm lightly over the shelf.
A more advanced technique is to fire the freshly applied glass separator to around 1000 degrees F. After the shelf cools, rub grit cloth over the glass separator. (Grit cloth is similar to sand paper except that it is an abrasive-coated mesh that allows residue to pass through. It can be rinsed with water and reused many times.)
As you rub the glass separator, watch the haik brush strokes in the surface. Remove just enough glass separator to remove the brush strokes. It takes just a moment to smoothen the surface.
I would appreciate knowing how this works for you.
With best wishes,
Arnold Howard Paragon Industries, L.P. - Better Designed Kilns 2011 South Town East Blvd. Mesquite, TX 75149-1122 Voice: 972-288-7557 & 800-876-4328 / Fax: 972-222-0646 firstname.lastname@example.org / www.paragonweb.com