Working Boro Tubing: The Basics of Points, Collapse Control, and Blowing Hollow
Short answer: Tubing work is rod work plus one new opponent — surface tension, which is constantly trying to collapse your hollow glass shut — and one new ally, air pressure, which pushes back from the inside. Your three controls are heat, rotation, and air: heat decides where the glass moves, rotation keeps the wall even, and a puff through a blow hose (or a sealed end) keeps the tube round instead of shrinking. The first skill to drill is pulling points; the constant goal underneath everything is even wall thickness. For starter stock, forum consensus clusters around heavy-wall 25mm x 4mm tubing, with 9–12mm heavy wall for blow tubes.
From rod to tubing: what actually changes
If you’ve been working solid rod, the flame itself doesn’t change — both rod and tubing must be introduced to the flame slowly, with consistent rotation, or they’ll crack from thermal shock (The Crucible, Lampworking 101). What changes is what the glass is for: rod is the material of solid, sculptural, and pictorial work; tubing is the basis for vessels, hollow beads, and functional work.
There are two routes to hollow flameworked glass: start with hollow tubing and reshape it with heat, or build a neck on a small steel blowpipe from a hot gather (The Crucible, Lampworking 101). Almost all boro flameworkers take the first route.
The material is the same borosilicate 3.3 you know from rod: mean linear thermal expansion 3.3 x 10⁻⁶/K, annealing point 560 °C, strain point 518 °C, softening point around 825 °C (SCHOTT DURAN datasheet). Boro 3.3 (DURAN, Simax, Pyrex-type) is specified by ISO 3585 and ASTM E438 Type I Class A, and that low expansion is what makes hollow work practical at the torch.
Why tubing collapses: surface tension never stops
Heat a section of tubing to working temperature and just watch: the diameter shrinks. That’s surface tension pulling the molten glass toward the smallest surface it can manage — the same force industrial tube-collapsing processes rely on deliberately, and which they counteract with internal air pressure when they want to keep the tube circular (US Patent 5,090,978).
For you, this cuts both ways:
- Collapse is a tool. Letting a heated section constrict is exactly how you pull a point, thicken a wall, or close an end.
- Collapse is the enemy. Any time you soak heat into tubing without either working fast or supplying air from inside, the bore shrinks and the wall slumps — usually unevenly.
Tubing work is really the craft of deciding when to let surface tension win and when to push back — the force itself runs whenever glass is soft.
The heat–rotation–air triangle
You have three controls, and every tubing operation is some combination of them.
| Control | What it does | What goes wrong without it |
|---|---|---|
| Heat | Decides which glass can move at all | Cold glass cracks; overheated glass slumps and collapses |
| Rotation | Distributes heat so the wall stays even | Lopsided wall: thin side blows out, thick side won’t move |
| Air | Counteracts surface tension from inside | The bore shrinks shut; blown sections go thin and pop |
Rotation deserves the most attention for rod converts. The ILPI Scientific Glassblowing tutorial defines it simply as continually turning the tubing or rod while it’s in the flame or softened — but on tubing the penalty for stopping is much harsher than on rod. If tubing isn’t rotated and heated evenly, the wall goes lopsided: thick on one side, thin on the other. The thin side becomes a hot spot that blows out; the heavy side becomes a cold spot that refuses to move (ILPI, Lessons 2 and 10). ILPI states the goal outright: maintain even wall thickness throughout the piece, because uneven walls will not reach working temperature uniformly.
Air arrives via a blow hose in most bench setups: a length of tubing that lets you deliver air into the piece while both hands stay on the glass, usually with a swivel assembly so you can keep rotating while you blow (The Crucible, tools and supplies guide). Early on you’ll also blow directly through the open end of a point.
Pulling points: the first skill to drill
A “point” is a section of tubing drawn down into a thin handle, and pulling them is the gateway skill. The ILPI test-tube tutorial lays out the sequence:
- Heat a section of the tubing while rotating until it softens — ILPI’s benchmark is the consistency of a cooked noodle — and let it constrict to about half its original diameter.
- Remove it from the flame, keep rotating, and slowly pull the ends about six inches apart. The soft section stretches into a narrow neck.
- Burn the pulled section off in the middle, leaving two pointed halves.
Every part of that sequence is the triangle in action: heat on one zone, rotation keeping the constriction symmetrical, surface tension doing the constricting before you stretch. Drill it on cheap clear tubing until the neck comes out straight and centered — a crooked point telegraphs uneven rotation, and everything built on that point inherits the wobble.
Sealing an end without wrecking the wall
To blow anything, the tube needs a closed end, and the usual route is through a point: draw the neck down, then melt it shut at the tip. The hazard is wall thickness — heat concentrated on a shrinking tip piles glass up in some places and starves it in others, and ILPI’s rule applies with full force here: if the sealed end’s wall is uneven, it won’t heat uniformly, and the thin zones will fail first when you blow.
The principle that heat plus compression builds wall is worth internalizing early. The classic demonstration is the maria: a ring of thickened glass made by heating tubing and pushing the ends together while rotating — ILPI’s standard is solid glass, no trapped air line, at least twice the wall thickness of the tubing (Lesson 16). Pushing in thickens, pulling out thins, and both happen exactly where the glass is hottest.
Blowing out a bubble without blowing a hole
With an end sealed, the beginner move is blowing a bubble at the tip. The instinct is one big breath; the ILPI tutorial says the opposite — blow the bubble in at least two steps, building up wall thickness near the body of the piece rather than committing everything to one blow (Lesson 10, Making a Test Tube).
The reason is wall-thickness logic again: a bubble stretches the wall thinner as it grows, and it grows fastest wherever the wall is thinnest or hottest. Small puffs let you watch where the glass is moving and re-heat between blows; one big blow into a very hot end gives you no chance to correct — the thin spot runs away and pops.
What tubing to buy first: sizes and wall thickness
Tubing is specified as outside diameter x wall thickness, and the wall matters as much as the diameter. The common American “heavy wall” starter spec is nominally 25.4mm OD x 4.0mm wall (inside diameter around 17.4mm). A 25mm x 1.5mm standard-wall spec also exists and is a different animal for a beginner — thin wall heats fast, collapses fast, and punishes slow hands.
Experienced workers on the Lampwork Etc. forum converge on heavy wall for starting out:
| Size (OD x wall) | Suggested use (per forum consensus) |
|---|---|
| 25 x 4 mm / 25 x 3 mm heavy wall | Marbles, implosions, wigwags; the general-purpose starter |
| 9–12 mm heavy wall | Blow tubes / handles |
| 20–26 mm medium wall | Hollow beads and tube implosions |
The heavy 25x4 gives you enough glass in the wall to survive uneven heating while you’re learning rotation, and enough mass to practice points, seals, and bubbles on the same stick.
Editor’s note: starter-size advice is genuinely contested. The heavy-wall 25x4 / 25x3 recommendation dominates for marbles and implosion-style work, but some experienced workers specifically recommend 20–26mm medium wall for hollow beads and tube implosions. Buy for what you actually want to make first, and treat the table above as a range, not a rule.
Heat management: how hollow work differs from solid
On rod, heat management is mostly thermal shock on the way in and even soak once working. Tubing keeps both and adds a third dimension: the wall is thin, so heat moves through it fast and unevenly.
- The margin for parked heat is smaller. A rod soaks; a tube collapses. Time out of the flame is part of the technique, not a break.
- Uneven heat shows up in seconds. ILPI’s lopsided-wall failure mode — thin-side blowout, thick-side cold spot — punishes a lapse in rotation almost immediately.
- Everything is a wall-thickness decision. Push in to thicken, pull or blow to thin, and keep the changes symmetrical with rotation.
The Corning Museum of Glass maintains free LibGuides that cover exactly this ground — “Working with Tubing and Hollow Flameworking” (basic operations, fundamental seals, practice pieces) and “Borosilicate Flameworking” (flame settings, making a gather, cold seals) — and they pair well with the ILPI tutorials as structured practice sequences. For a broader learning path, see how to learn lampworking.
Torches that handle boro tubing
Boro tubing wants the same thing boro rod wants — a flame with real punch — plus enough flame width to keep a band of tubing evenly hot while you rotate. Entry boro-capable torches like the GTT Bobcat will handle small tubing work; larger hollow pieces push you up the range. Rather than repeat the full rundown here, see best torch for borosilicate for picks by budget and size of work, and match the torch to your oxygen supply before you buy.
When it cracks anyway: stress, flame chemistry, and the kiln
Tubing pieces crack for the same reasons rod pieces do — thermal shock on the way into the flame, and residual stress if the piece cools unannealed — but the thin, uneven walls of learner tubing work concentrate stress in ways solid work doesn’t. If your practice pieces keep failing, work through why did my glass crack first.
For annealing, the boro 3.3 reference figures are the SCHOTT DURAN numbers above: annealing point 560 °C, strain point 518 °C. Notably for tubing workers, SCHOTT’s annealing schedule varies the cooling rate by wall thickness (rates given for 3mm, 6mm, and 12mm walls) — the wall you chose at purchase follows you all the way to the kiln. Full schedules are in annealing schedules for glass. Figures here are manufacturer-datasheet reference values — your kiln manual and glass manufacturer’s documentation take precedence for your setup.
Key takeaways
- Tubing adds surface tension (always collapsing your tube) and air pressure (your push-back) to the rod skills you already have; the controls are heat, rotation, air.
- Even wall thickness is the goal; uneven walls won’t reach working temperature uniformly, and rotation failures show up as thin-side blowouts and thick-side cold spots.
- Drill pulling points first: soften to cooked-noodle consistency, constrict to about half diameter, pull about six inches out of the flame, burn off in the middle.
- Blow bubbles in at least two steps, building wall near the body — never one big blow.
- Start with heavy-wall 25 x 4mm (or 25 x 3mm) plus 9–12mm blow tubes; medium-wall 20–26mm has advocates for hollow beads — the advice is contested, so buy for your first project.
- Anneal to the manufacturer’s schedule; cooling rates vary by wall thickness.
Sources
- ILPI Scientific Glassblowing Learning Center, Tutorial Lesson 10, “Making a Test Tube” — https://www.ilpi.com/glassblowing/tutorial_testtube.html
- ILPI Scientific Glassblowing Learning Center, Tutorial Lesson 2, “Terminology” — https://www.ilpi.com/glassblowing/tutorial_terms.html
- ILPI Scientific Glassblowing Learning Center, Tutorial Lesson 16, “Ring Seals” — https://www.ilpi.com/glassblowing/tutorial_ringseal.html
- Corning Museum of Glass LibGuides, “Working with Tubing and Hollow Flameworking” — https://libguides.cmog.org/pipe_making/hollow_work
- Corning Museum of Glass LibGuides, “Borosilicate Flameworking” — https://libguides.cmog.org/flameworking/boroflameworking
- SCHOTT, DURAN tubing product and technical data — https://www.schott.com/en-us/products/duran-p1000368
- The Crucible, “Lampworking 101” guide — https://www.thecrucible.org/guides/lampworking-flameworking/
- Lampwork Etc. forum archive, “Suggested tubing sizes?” — https://www.lampworketc.com/forums/archive/index.php/t-214087.html
Editor’s note: glass property figures are from the SCHOTT DURAN datasheet for borosilicate 3.3 and may differ slightly between brands; starter tubing-size advice is community consensus from forum threads and genuinely varies by intended work. Follow your glass and kiln manufacturers’ documentation over any figure here.