A parison becomes a vessel in five finishing moves: marver to centre it, jack a neck, transfer it to the pontil, reopen and shape the rim in the glory hole, then crack it off and put it straight into the annealing oven. Every move must be done while the glass is still soft, which gives about 30 seconds per heat. The piece is not finished until it is annealed, because unannealed glass cracks within hours.
Part of Glass Blowing and Forming
The finishing sequence that turns a blown parison into a usable open vessel.
Finishing Is A Run Of Short Heats With Two Clean Breaks, Not A Single Pass
The carrier’s description gives the sequence, and says that without reheating the glass stiffens in roughly 30 seconds. This article adds the reasons.
What You Need
- A parison from Bubble Formation.
- Marver, jacks, a pontil and wet tools; see Shaping Tools and Pontil and Punty.
- The glory hole running, and the annealing oven at hold temperature.
Method: From Parison To Finished Vessel
Step 1: Marver. Roll the piece on the marver to cool the skin and shape it. The glassblowing article says the marver also presses out surface irregularities.
Step 2: Jack a neck. Squeeze a constriction at the point where the piece will leave the pipe.
Step 3: Transfer to the pontil. Attach a pontil rod carrying a small gather to the base. Touch a wet tool to the neck to crack the blowpipe off the top. Now the opening is accessible.
Step 4: Open the top. Reheat the cracked-off end and widen the opening with jacks.
Step 5: Shape the rim. Flatten, flare or thicken it as needed. A fire-polished rim is made by reheating until surface tension rounds it over.
Step 6: Crack off the pontil. Touch a wet tool to the attachment point and tap.
Step 7: Anneal immediately. The carrier says unannealed glass will crack within hours.
Common Mistakes
- Working the lip too cold. The glass cracks when forced.
- Not keeping the piece turning during transfer. It sags before the pontil is attached.
- Leaving the piece on the bench to cool. It goes to the oven at once.
Safety
Hot glass does not look hot
A crown, rim or detached piece below about 600 °C shows no glow but burns skin. Handle it with tongs and put it on a marked tray or into the oven.
Cracking off throws shards
Both separations throw hot fragments. Wear eye protection and keep the floor clear.
What’s Next
- Learn next: Annealing Oven (Lehr) — where the finished piece goes
- Combine with: Mold Blowing — repeatable shapes