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Encasement Without Bubbles: Trapping Color, Not Air

Why encasement traps bubbles (cold layers, wrap seams, deep valleys) and how to avoid them: wrap-and-melt, gather-over, boro layering, and heat fixes.

cluster · published

By Glass Torches Editorial · Updated

Encasement Without Bubbles: Trapping Color, Not Air

Short answer: Bubbles get trapped in encasement for one root reason: somewhere, glass met glass without being molten enough to exclude the air between them. The fixes follow from that. Keep the base piece properly warm, apply the clear very molten and press it firmly against the glass already there, close every wrap seam before adding the next layer, and fill deep valleys in the surface instead of bridging over them. In soft glass that means a careful wrap-and-melt or a committed gather-over; in borosilicate it means layering clear over color with enough heat that any trapped air resolves cleanly. And when a bubble does sneak in, heat, a marver, and a pick can often chase it out.

If you are still choosing your clear, read the clear boro quality guide for hard glass and soft glass brands explained for soda-lime. A dirty or scummy clear will sabotage even perfect technique.

What a bubble actually is: seeds vs. air traps

The Corning Museum of Glass defines a bubble simply as a pocket of gas trapped in the glass. The term covers both intentional decorative bubbles (air traps, placed on purpose) and unwanted bubbles; very small unwanted ones are traditionally called “seeds.” Source: Corning Museum of Glass.

For encasement work it helps to separate two mechanisms:

  • Mechanically trapped air: air physically enclosed where two glass surfaces met, at a wrap seam, over a valley, or under a layer applied too cold. This is the main subject of this article, and it is preventable with technique.
  • Boiling: micro-bubbles generated by the color itself when it is overheated. Forum reports name certain bright opaques and some whites as common culprits, though this is anecdotal rather than a definitive list. Boiling is a heat-management problem, not a layering problem.

Why encasement traps air: cold layers, seams, and valleys

Three situations account for most trapped bubbles:

  • Cold layers. If the base piece has cooled too far, or the clear is not fully molten when it lands, the two surfaces cannot flow together and air stays between them. Dark colors are especially demanding: when encasing black, the base bead should be warmer than usual, with the glow having only just faded, or the clear will scum. At the same time the base must not be so hot that it distorts, so experienced encasers cycle the glow out of the bead periodically to keep it stable. Source: Laura Sparling.
  • Wraps meeting. Every place where a coil of clear starts, stops, or crosses another coil is a potential seam. If wraps are laid down with gaps and then melted from above, the glass bridges the gap and seals a line of air underneath.
  • Deep valleys. Raised decoration (dots, stringer lines, twisted cane) creates valleys between the raised elements. Clear applied across the tops of those features roofs over the valleys and traps air in every low spot. The valley has to be filled with molten glass, not bridged.

The single preventive principle behind all three, repeated by working lampworkers for decades, is to encase with very molten glass pressed firmly against the glass already there. Molten glass that is pushed into contact excludes air; glass that is draped or bridged over a surface traps it. Source: Lampwork Etc..

Soft glass, method one: wrap and melt

The wrap-and-melt is the standard first encasing method for soft-glass beadmakers. You wind thin wraps of molten clear around the base bead, then melt them smooth. The bubble rules:

  • Start every wrap on a smooth base. A wrap that begins on an irregular or gapped surface traps air at its starting point.
  • Close gaps before adding more glass. If your coils end up gapped, gently reheat them and press them together with a tool so the seam closes, then add the next layer. Never melt a fresh layer over open gaps.
  • Touch edge to edge. The edge of each new wrap of glass should touch the edge of the glass already laid down, so the advancing molten front pushes air ahead of it instead of enclosing it.

Source: Laura Sparling, Basic Encased Bead.

A midrange soft-glass bench burner such as the Nortel Minor or GTT Cricket has no trouble keeping both the base bead warm and the clear rod workable for this method; the challenge is hand discipline, not heat.

Soft glass, method two: the gather-over

For thick, optically deep encasement, wraps become tedious and seam-prone. The gather-over method applies the clear in one committed move. Keep the base bead warm, heat a gather of clear until it is fully molten, then press the gather onto the bead and spread it across the bead’s width while slowly turning the mandrel away from the gather. Because you are always pressing molten glass against existing glass, air is excluded as you go.

Laura Sparling’s rule of thumb is a gather roughly three times the size of the base bead. Treat that as one artist’s starting point rather than a universal standard; the right gather size depends on the bead and on how thick you want the clear layer. Source: Laura Sparling, Basic Thick Encasing.

MethodBest forMain bubble riskKey habit
Wrap and meltThin, even encasement; beginnersAir sealed under gapped or crossed wrapsClose every seam before the next layer
Gather-overThick, optically deep encasementA gather that is not fully moltenPress and spread, never drape
Boro clear-over-colorHard-glass layered workCold clear over textured colorHigh heat so trapped air resolves round

Boro is different: clear over color at higher heat

Borosilicate encasement follows the same air-exclusion logic but with two hard-glass twists.

First, boro’s higher working heat is your friend. Air trapped during boro encasement will resolve into round bubbles, rather than lines and streaks, if sufficient heat is used, and a small round bubble is far easier to work out (or live with) than a smeared streak of trapped air. That description comes from a Pittsburgh Glass Center class listing rather than a technical paper, so treat it as practitioner knowledge, but it matches how boro encasers work: melt the clear in hot and thoroughly. This heat-heavy melt-in is where a torch with real output, such as a GTT Bobcat or Nortel Major, earns its keep.

Second, boro colors have per-color encasement behavior documented by the manufacturers, and that documentation takes precedence over any general advice:

  • Northstar Glassworks advises working colored boro in a neutral to slightly oxidizing flame to keep color vibrant, warns that deep encasement of certain colors (NS-104 Unobtainium is their example) can cause cracking, notes that heavily encased work must be annealed thoroughly, and documents color shifts under clear, for example that Amber/Purple encased in clear cannot show its purple highlights. Source: Northstar quick guide.
  • Glass Alchemy publishes per-color notes as well: Agua Azul 446, for instance, is documented as working great in encasement, worked in a neutral flame, garaged at 975 F and annealed at 1050 F. Source: Glass Alchemy.

So avoid the blanket claim that boro colors crack when encased deeply. Some do. Check the manufacturer’s color notes before burying a color under thick clear, and follow the maker’s annealing figures, not generic ones.

Chasing bubbles out: heat, marver, and pick

A trapped bubble is not always a lost cause. Working lampworkers use a short ladder of fixes, roughly in order of aggression:

  1. Heat cycling. In simple beads, cycling the piece between orange-hot and cooler encourages trapped bubbles to rise to the surface and work themselves out.
  2. Push it out with the rod. A fresh, shallow bubble can often be pushed out with the stiff part of the glass rod while the surface is soft.
  3. Marver it. Rolling the whole molten bead on a marver can pop bubbles at or near the surface.
  4. Open it with a tungsten pick. For a stubborn bubble, pick it open and push glass into the void, then melt the repair smooth.

Source: Lampwork Etc., “Bubbles, how do you get rid of them?”.

Two cautions. Chasing bubbles with extreme heat risks boiling the underlying color layer and can shift striking colors, so escalate gradually. And if the glass itself starts boiling in the flame, pull the bubbly tip off with tweezers and continue in a cooler part of the flame rather than fighting it. Prolonged superheating sessions also make the standard flameworking safety points, didymium eyewear and active ventilation, matter more, not less; see the glass torch safety setup guide if your station is not squared away.

Clear quality matters as much as technique

Soft-glass clear is brand- and batch-dependent. Effetre 006 Super Clear has documented batch variability with bubbling and scumming, was reportedly reformulated in 2017 for better clarity (a claim from forum discussion, not a manufacturer statement), and benefits from being worked slightly cool. Some encasers prefer Double Helix Zephyr for critical clear layers. Rankings vary by batch and by artist, so treat any “best clear” claim as provisional and test the rod in your hand. The soft glass brands guide covers the landscape, and the clear boro quality guide does the same job for hard glass.

When bubbles are the point

Deliberately trapped air is an established design technique, not a failure state. The plunge method superheats one spot, plunges a cool poker in to form a divot, and then, once the glow fades, swipes a hot rod or clear over the hole rather than into it, sealing air inside. Clear glass suspends the bubble visually better than plunging directly into opaque color. Source: Lampwork Etc..

Implosion pendants take this further: the whole technique exploits encasement depth deliberately, and many boro artists value the bubbles achievable in imploded work as part of the aesthetic. See the implosion pendant technique guide for the full method; pinpoint-flame torches like the GTT Lynx suit that kind of detail work.

One boundary on “bubbles are fine”: beadmaking sources note that bubbles do not compromise the structural integrity of a solid encased bead. Do not extend that to functional or blown boro, where a bubble in a thin wall can be a weak point.

Key takeaways

  • Bubbles come from glass meeting glass without enough heat: cold layers, open wrap seams, and bridged valleys are the three classic traps.
  • The universal preventive habit is to encase with very molten glass pressed firmly against the glass already there.
  • Soft glass: wrap and melt with every seam closed, or gather-over with a fully molten gather pressed and spread across the bead.
  • Boro: melt clear in with generous heat so trapped air resolves round, and check manufacturer per-color notes before deep encasement; some colors crack, and heavily encased work needs thorough annealing per the maker’s figures.
  • Fixes escalate from heat cycling to the rod push, the marver roll, and the tungsten pick, but extreme heat can boil color layers.
  • Bubbles can be a feature: plunged bubbles and implosion work trap air on purpose.

Sources

Editor’s note: technique guidance here reflects published tutorials, manufacturer color notes, and community practice as of 2026. Gather sizes, flame chemistry, and annealing figures vary by glass and by artist; where manufacturers publish per-color or annealing guidance, their documentation takes precedence over anything written here.

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Sources