Bullseye Glass Mold #8929, Rectangular Slumper

The Rectangular Slumper mold from Bullseye Glass (design #8929) is a large-format kiln form for slumping pre-made glass sheets or fused blanks into a rectangular tray or shallow dish shape. Place a cut sheet or fired piece over the mold, load it into the kiln, and let the heat soften the glass so gravity draws it down onto the form.

The outer dimensions are 16.5 inches by 11.9 inches by 2 inches tall (42 x 30 x 5 cm). These are the outer mold dimensions used to confirm the piece will fit your kiln shelf. Because each mold is handmade, individual pieces vary slightly in size, so measure the actual mold before cutting your glass. The mold is slipcast from a specially formulated clay body by Creative Ceramics in Europe and imported by Bullseye Glass. The surface is exceptionally smooth, accepts kiln wash uniformly, and does not crack under repeated proper use.

What does the Rectangular Slumper mold make?
It slumps a flat glass sheet into a rectangular tray or shallow dish form. The shape and depth of the slump follow the mold contour and depend on the firing temperature and hold time.

What COE glass can I use with this mold?
Any COE. The ceramic mold is COE agnostic, so you can slump COE90, COE96, or other fusible glass in the same form. Match your firing schedule and anneal soak temperature to the glass you are using.

How do I prep the mold before firing?
Coat the forming surface with a kiln wash such as Hotline Primo Primer or a shelf primer and let it dry completely before placing your glass. The smooth surface accepts kiln wash uniformly. Re-coat as needed between firings.

How do I know what size glass to cut?
The listed dimensions are the outer mold dimensions for checking kiln fit. Because these molds are handmade and vary slightly, measure the actual mold you receive before cutting glass for it.

Specifications

• SKU: 170191
• Manufacturer: Bullseye Glass (BG8929; made by Creative Ceramics, imported by Bullseye)
• Makes: rectangular slumped glass form
• Outer mold size: 16.5 inches L x 11.9 inches W x 2 inches H (42 x 30 x 5 cm)
• Sizing note: molds are handmade and vary slightly in size; measure before cutting glass
• Material: slipcast ceramic kiln form, reusable
• Glass: any COE (COE agnostic)

Working Notes

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

• Coat the forming surface with kiln wash or a shelf primer such as ZYP Boron Nitride Mold Primer, and let it dry completely before placing glass on the mold.
• Place your pre-cut glass sheet or fused blank centered over the prepared mold surface and load the kiln.
• The mold is COE agnostic. Use a slumping schedule matched to your glass. The anneal soak temperature in the schedule below suits COE90; for COE96, raise the anneal soak to about 950 F.
• Let the kiln cool fully before removing the slumped piece. Re-coat the mold with kiln wash as needed between firings.

Bullseye Suggested Slumping Schedule

This schedule is a suggested starting point based on slumping 6mm pieces in a Paragon GL24 kiln, 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, kiln, and mold depth.

*AFAP means as fast as possible, letting the kiln drop at its natural rate with the door closed. The 900 F anneal soak in Segment 2 suits COE90. For COE96, adjust the anneal soak to about 950 F.

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

Description updated: July 6, 2026

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