The Scientific Glassblowing Learning Center: Tutorial Lesson 12, T Seals
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T Seals
T seals are simply two tubes sealed together at right angles. Modified T seals may have the glass tubes at any angle degree, but the basic technique is the same. Joining dissimilar sized tubes end to end may be more appropriately classified as butt seals, but for our purposes are carried in this section because the technique shown is similar to the T seal.
- Clamp a sealed 10 mm tube horizontally in a ring stand. Attach a blowhose assembly to the open end of the tube.
- Light and adjust the torch to a sharp flame. Remove the torch from the holder.
- Heat a 10 mm spot on top of tube.
- Remove the torch flame and blow out a bubble about 10 mm in diameter (do not pop it).
- Reheat the bubble and let the glass collapse to a flat even plateau and remove the torch. The sides of the plateau should be about 3 mm high.
- Reheat the plateau, remove the torch and blow a second bubble, (don't pop it yet...patience!).
- Position the flame to cross over the top of the bubble, blowing hard at the same time to pop bubble.
- Melt the glass down evenly, forming a hole 10 mm in diameter with level 3 mm high side walls.
Tip: Re-blowing the bubble in steps 5 and 6 helps build up the wall thickness at the point where the second tube is sealed. It is important not to skip this step! If you have performed steps 3 -8 correctly you should have a very close match of the ID and OD of the hole in tube #1 to the end of tube #2. Use a second 10 mm piece of tubing as the leg that will be attached to tube #1. We will attach this in the same fashion as the stationary buttseal that we performed in the previous lesson:
- Hold tube #2 above and at a slight angle to the 10 mm hole in tube #1 you have blown in step 8.
- Move the torch flame back and forth across the rear of the hole and the leg.
- Bring the back of tube #2 down onto the back of the hole in tube #1.
- Continue heating and bring tube #2 forward in a continuous smooth motion, making complete contact with the base.
- Work out the seal a small section at a time (see step 7 of stationary butt seals).
- Anneal. Remember, a glassblowing job is never complete until the glassware is annealed!
Troubleshooting T Seals
| Looks Like | Cause and Correction |
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Seal is blown out too far. Use asmaller flame concentrated exactly on the seal area. Avoid flame splash on the tubing away from seal. |
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Seal is constricted - not blown out enough. Use a sharp flame to heat the restricted area and blow it out to a consistent tube ID. |
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Seal is lumpy and/or uneven. The seal was not heated hot enough to flow the glass. Reheat the seal with a sharp intense flame. |
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(a) Seal has uneven wall thickness. The tube was heated excessively causing glass to flow with gravity. (b) Reorient tube. (c) Reheat seal, gravity flow to correct. |
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Leg is tilted - too much heat was applied over a large area. Use a sharper flame and heat small sections at a time. Of course, if your intent was to create an angle seal of about 45 degrees - well done! |
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Hole! Did not seal completely or blew too hard creating hole. (a) Small hole - Heat the end of a 2 mm rod red hot and quickly stick and pull rod end into hole, sealing it shut. Work out seal. (b) If the hole is large, you may have to add glass by "weaving" the hole shut, again use 2 mm rod. Try to avoid using an excessive amount of glass with this method. (c) Use a tungsten pick to "sew" the hole shut. Heat only the glass, not the pick. Avoid creating thin spots using this method. |
Advanced version
There is a variant of the T-seal technique called suck seals. We mention it here so you are aware of it, but the method discussed here is the preferred one, and the one that you need to master!