Cut or machined acrylic has a rough, frosted edge that obscures the material's natural clarity. Polishing restores that clarity, transforming a cloudy saw-cut edge into a crystal-clear, glass-like surface. The process is simple: sand through progressively finer grits, then buff with compound. Here is how to do it properly for cast acrylic sheet and other acrylic products.
Wet sanding
Start at a grit that matches the roughness of your starting surface. For bandsaw or jigsaw cuts, start at 240. For router-cut edges, you can often start at 400. For laser-cut edges, start at 600 — the laser leaves a smooth but slightly frosted surface.
Use wet-and-dry (silicon carbide) paper with water as a lubricant. Sand in one direction only at each grit (not circular), then change direction by 90 degrees at the next grit — this makes it easy to see when you have fully removed the scratches from the previous grit. Progress through: 240 → 400 → 600 → 800 → 1000 → 1500 → 2000. Do not skip grits in the early stages — each grit removes the scratches from the one before, and skipping leaves deep marks that become visible at the polishing stage.
Keep the surface and paper wet throughout. Dry-sanding acrylic generates heat that can melt the surface and create smears that are very difficult to remove.
Polishing compound
After 2000 grit, switch to a polishing compound. Apply a small amount to a soft cotton cloth or a foam polishing pad and work the surface with moderate pressure in overlapping circular motions. A dedicated plastic or acrylic polish gives the best results, but a fine automotive cutting compound works well too.
For machine polishing (which is significantly faster for large surfaces or many pieces), use a buffing wheel on a bench grinder or a foam pad on a rotary polisher. Keep the acrylic moving against the wheel — holding it in one spot generates heat and can melt or distort the surface. A light touch and steady movement produce the best results.
Flame polishing
Flame polishing is a fast method for achieving clear edges on acrylic without sanding. A hydrogen-oxygen torch or a small butane torch is passed quickly along the edge — the heat melts the surface layer, which flows smooth and re-solidifies as a clear, glossy surface.
This technique requires practice. Move the flame quickly and evenly — too slow and the acrylic bubbles, warps or catches fire; too fast and the surface does not melt enough to clear. Flame polishing works best on straight edges of uniform thickness. It is not suitable for curved or detailed edges, and it can introduce internal stresses that cause crazing (fine surface cracks) over time if the heating is uneven.
For most makers, wet sanding and compound polishing gives a more consistent, controllable result than flame polishing.
Tips
Cast acrylic polishes to a higher clarity than extruded acrylic — cast has fewer internal stresses and a more uniform molecular structure. If optical clarity matters, use cast sheet. Clean polished acrylic with a soft microfibre cloth — paper towels and rough cloths scratch the surface. Anti-static cleaner reduces dust attraction on the finished surface.
