The Square Slumper B with Flat Base mold from Bullseye Glass (design number 8998) is a compact ceramic slumping form that shapes a pre-cut or pre-fused glass sheet into a small square piece with a flat bottom. Glass is placed over or into the form and fired so it softens and settles by gravity, conforming to the square shape and leaving a level base once cooled.
The mold outer dimensions are 3.4 inches by 3.4 inches, with a depth of 0.9 inches (9 by 9 by 2 cm). These measurements are the outer size of the mold, given for checking kiln fit. Because each mold is handmade by Creative Ceramics in Europe from a specially formulated slipcast clay body, individual pieces vary slightly, so measure the actual forming surface before cutting glass. The surface is exceptionally smooth and accepts kiln wash uniformly, making prep consistent across firings. The mold is reusable with proper care.
What does this mold make?
What size glass should I use?
What COE glass works with this mold?
How do I prep the mold before slumping? Hotline Primo Primer or a shelf primer and let it dry completely before placing glass. The smooth surface accepts kiln wash evenly. Re-coat as needed between firings.
Specifications
SKU: 3667Manufacturer: Bullseye Glass (slipcast by Creative Ceramics in Europe, imported by Bullseye Glass; design number 8998, item 008998-MOLD-M-EACH; store code BG8998)Makes: 1 square slumped piece with flat baseMold outer dimensions: 3.4 in L x 3.4 in W x 0.9 in H (9 x 9 x 2 cm)Note on sizing: molds are handmade and vary slightly; measure the forming surface before cutting glassMaterial: slipcast ceramic kiln mold, reusableSurface: exceptionally smooth, accepts kiln wash uniformlyGlass: 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 kiln wash or a boron nitride mold primer such as ZYP Boron Nitride Mold Primer , and let it dry completely before placing glass.
Measure the actual forming surface of your mold before cutting glass. The outer dimensions (3.4 by 3.4 by 0.9 inches) are for checking kiln fit; the forming area is smaller and varies between handmade pieces.
Place your pre-cut or pre-fused glass blank onto or into the form. For this shallow square form, a single layer of glass or a pre-fused piece slumps cleanly into shape.
The mold is COE agnostic. Use a slumping schedule matched to your glass, and adjust the anneal soak temperature for your COE (about 900 F for COE90, 950 F for COE96).
Visually confirm the slump during firing so you can catch the glass at the right point. Let the kiln cool fully before removing the piece. Re-coat the mold with kiln wash as needed between firings.
Bullseye Suggested Slumping Schedule
This is a suggested starting schedule based on slumping 6mm pieces in a Paragon GL24, not a guarantee. Every kiln fires differently. Test a small piece first and follow Bullseye's published guidance for your glass and mold depth.
Segment Rate Temp (F) Hold 1 (slump) 300 F/hr 1200 :10 2 (anneal soak) AFAP 900 1:00 3 (anneal cool) 100 F/hr 700 none 4 (cool) AFAP 70 none
AFAP means as fast as possible, at the kiln's natural rate. This schedule is based on 6mm glass in a Paragon GL24. Adjust for thicker pieces with a slower ramp and longer anneal soak. The anneal soak in segment 2 is at 900 F, suited for COE90; raise it to 950 F for COE96.
Helpful downloads: Suggested Slumping Schedules from Bullseye Glass (PDF)
Description updated: July 6, 2026
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