Glass Cups Part 2 of 2: Making the Cup

Length of Project:
Project theme:
Suitable for grades:
Tools & Materials
Material List
  • glass bottles (3+)
  • wet-dry sandpaper, various grits 80-400+
  • dish soap
  • Optional

  • printed photo or design for etching step ~3" x 3"
  • masking tape
Tool list
  • safety glasses
  • work gloves
  • dust mask
  • Glass Cup Cutting Jig from Part 1 of this project
  • rotary glass cutting tool
  • candle
  • lighter or matches
  • large jug or sink of ice water
  • glass disposal bin
  • paper towel or rag
  • flat surface (table top or piece of laminate)
  • Optional

  • electric rotary tool and etching bit
  1. Prepare your ice water: fill a jug or sink halfway with cold water and add a handful of ice to it. Make sure it is deep enough to submerge your bottle below the cut line.
  2. Position your jig with the end piece braced against a wall or solid object, or secure it in a vise. Line a bottle up in the jig with the bottom against the end piece.
  3. Put on your safety glasses and gloves. Place your glass cutting tool into the groove in the jig.
  4. With one hand (or both hands, if you’ve got a buddy to help you), push the bottle hard against the plywood end piece of the jig and rotate the bottle slowly around. With the other hand (or have your buddy to do this part), press the glass cutter firmly down into the side of the bottle. Press hard enough to hear the glass being scored by the cutting tool; rotate the bottle until you can see a continuous score line all the way around the bottle.
  5. Light the candle, then rotate the bottle just above the flame slowly, heating the score line made in the previous step. Keep rotating and heating for about 30 seconds.
  6. Holding the bottle at the neck, bring it immediately from the candle to the icy water jug, pushing the heated score line below the water line. You might hear a crack or a tick sound as the glass breaks along the line. Avoid touching any edges of the glass when it breaks as it will be very sharp.
  7. If the bottom didn’t fall off in the water, remove it and wipe it gently with a rag or paper towel to clean away any soot. Inspect the score line: if it looks cracked through all along the score line, try gently twisting the bottle bottom and neck in opposite directions to pop the two pieces apart.
  8. If there are cracks in the glass other than right at the score line, like the photo, put your bottle in the glass disposal bin and try again with a new bottle.
  9. If you can see that the glass hasn’t cracked all the way through, you can try repeating the heating and cooling steps once more. If it doesn’t work, place it in the glass disposal bin and try again with a different bottle; don’t put your original bottle back into the jig, as it is liable to break unpredictably if you try to score it again.
  10. Repeat the above steps with several bottles as necessary until you have one with a flat cut (no large jagged edges that will take a long time to sand away). Place the bottle top in the glass disposal bin (or if you plan to etch your glass, save it to practice on.)
  11. Put on a dust mask, and make sure you are wearing gloves and safety glasses. Wet a piece of 80 grit wet-dry sandpaper, place it on a flat surface, and start sanding your sharp cup edge. Press gently, moving your cup in small circles (rotating it occasionally to make sure you sand it consistently around the lip).
  12. After about 1 minute of sanding, wipe the water off the lip with a rag or paper towel to check your progress. Keep sanding until the glass’s top edge is uniformly etched with no sharp, shiny areas (be patient, this first step may take ten minutes or more).
  13. Dress the top edge of the cup with a “flat polish”, making a very small bevel by sanding at a 45° angle to the top of the inside and outside of the cup with a sanding block. (To achieve a “pencil polish” edge, keep sanding until the edge is rounded with no hard corner.)
  14. Repeat the flat and bevel sanding steps with increasing sandpaper grits, finishing with 400 grit paper (or finer, if you choose). Carefully inspect the cup’s top lip visually for sharp edges, then test it by running a piece of fruit or food along all the edges to make sure it won’t cut you. Take it to your instructor for a final inspection and approval.
  15. To etch a design into your glass, insert an etching bit into a rotary tool. If you don’t want to freehand a design, you can print a picture and tape it inside the cup to trace along with the etching tool, or you can use masking tape to mark out designs to guide your etching.
  16. Be sure to wear your mask, safety glasses, and gloves for this step. Practice first on a spare bottle (or your discarded bottle top) to get used to the pressure and movements needed to achieve your desired etching effect. When you are feeling ready, place your glass in the jig and etch away!
  17. Rinse your cup under running water to remove glass dust. Wash and scrub it thoroughly with dish soap and a cloth before using it.
Extension Challenges
  1. Make a matching set of 4 or 6 glasses as a customized gift, or personalize a set for friends, family, or housemates so everyone knows whose glass is whose.
  2. Cut protective stencils out of thick, sticky-backed vinyl, then stick them to your cup. Use a sand blasting setup or etching cream to etch designs. Anywhere not protected by the vinyl will be etched by the sand particles or chemicals. Wash your glass thoroughly before use..
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