Bullseye Glass Mold #8637, Square Slumper A 12"

The Square Slumper A 12 inch mold from Bullseye Glass (design 8637) is a ceramic slumping form that shapes a flat glass blank into a shallow square dish or tray. A pre-cut or pre-fused sheet of glass is placed over or set into the form, then heated in the kiln until it softens and settles into the mold contour by gravity.

The outer dimensions are 12 inches by 12 inches by 2.2 inches (30 by 30 by 6 cm). These dimensions are used to check kiln fit. The mold is slipcast from a specially formulated clay body by Creative Ceramics in Europe and imported and sold by Bullseye Glass. Because each mold is made by hand, individual pieces vary slightly in size, so measure your specific mold before cutting glass. The forming surface is exceptionally smooth, accepts kiln wash uniformly, and the mold does not crack under repeated proper use.

What does the Square Slumper A 12 inch mold make?
It shapes a flat glass blank into a shallow square form roughly 12 inches across. Finished pieces work well as square dishes, trays, and decorative flat panels. The exact interior profile follows the mold contour and the degree of slump achieved during firing.

What glass can I use with this mold?
Any fusible glass. Ceramic slumping forms are COE agnostic, so COE90, COE96, and other fusible glass all work with this mold. Match your firing schedule and anneal soak temperature to the COE of the glass you are using.

How do I prepare the mold before slumping?
Coat the forming surface with a kiln wash or shelf primer and let it dry fully before placing glass. This prevents the softened glass from bonding to the mold surface. Re-coat between firings as needed.

How do I size the glass blank for this mold?
Use the outer dimensions as a guide to kiln fit, but measure your specific mold before cutting glass. These molds are handmade and vary slightly in size, so the usable forming area can differ a little between individual pieces.

Specifications

• SKU: 3655
• Manufacturer: Bullseye Glass (design 8637; made by Creative Ceramics, imported by Bullseye)
• Mold type: Square slumper
• Outer dimensions: 12 inches L x 12 inches W x 2.2 inches H (30 x 30 x 6 cm)
• Sizing note: molds are handmade and vary slightly; measure before cutting glass
• Material: slipcast clay body, reusable kiln slumping form
• Glass: any COE (COE agnostic)

Working Notes

These are guidelines, not guarantees. Every kiln fires a little differently, so test a small piece first when the result matters and follow a slumping schedule suited to your glass and kiln.

• Coat the forming surface with a kiln wash or shelf primer such as ZYP Boron Nitride Mold Primer and let it dry completely before placing glass, so the softened glass does not bond to the mold surface.
• Place your pre-cut or pre-fused glass blank over or into the form. Measure your specific mold before cutting glass, since handmade molds vary slightly in size.
• The mold is COE agnostic. Adjust the anneal soak in your firing schedule to match the glass you are using: about 900 F for COE90 (as listed in the schedule below) or 950 F for COE96.
• Visually confirm the slump during firing if your kiln allows, and remove from heat once the glass has fully settled into the mold contour.
• Let the kiln cool fully before removing the slumped piece. Re-coat the forming surface with kiln wash as needed between firings.

Bullseye Suggested Slumping Schedule

This is Bullseye's suggested starting schedule for slumping 6 mm glass in a Paragon GL24 kiln. It is not a guarantee. Every kiln fires differently and glass styles vary in viscosity. Visually confirm the slump during firing and adjust the schedule for your glass and kiln.

AFAP means as fast as possible, at the kiln's natural rate. Segment 4 is a natural cool with the door closed. Adjust the anneal soak temperature for your glass: about 900 F for COE90 or 950 F for COE96.

Helpful downloads: Suggested Slumping Schedules from Bullseye Glass (PDF)

Description updated: July 6, 2026

Spot an error or have feedback on this description? Report it here.