Dichro in Lampwork: Coated-Side Rules, Encasement, and Why Coatings Burn Off

Short answer: Dichroic glass is ordinary glass carrying an ultra-thin metal-oxide coating that creates color by optical interference, and that coating is the fragile part. At the torch the rule is simple: cap it or burn it. The flame should only ever touch the uncoated glass side; the coated face gets protected by applying it coating-down against your work, sealing every edge, and encasing it in clear. Buy dichro made on the same COE as your base glass (33, 90, 96, or 104), because the substrate, not the coating, determines compatibility. Work it with a cool, oxygen-rich flame, and the shimmer survives; hit the coating directly or starve it of oxygen, and it burns off into gray scuzz.

What dichroic coating actually is

Dichroic glass gets its shifting color from thin-film interference, not from pigment or dye. Dozens of ultra-thin layers of metal oxides (titanium, silicon, and magnesium oxides among them) are vacuum-deposited onto a glass substrate. Light reflecting off those stacked layers interferes with itself, so the transmitted color and the reflected color are different, and both shift as the viewing angle changes. That is why a single piece of dichro can flash gold, then blue, then magenta as you turn it. Sources: Wikipedia, Glass Tips.

The technology is a direct spinoff of aerospace optics. NASA’s Spinoff program documents how the thin-film coating techniques developed for satellite and instrument optics were adapted to decorative art glass. Source: NASA Spinoff.

Two practical consequences follow from the physics:

• The color layer is on one face only. Everything about handling dichro at the torch comes down to knowing which face that is and protecting it.
• The coating is vanishingly thin. CBS (Coatings by Sandberg), the dominant art-glass dichro manufacturer, tops its coatings with a quartz layer, but it is so thin that anything hard enough to scratch glass will scratch the coating too. CBS also advises scoring and cutting on the uncoated side for a cleaner break. Source: CBS.

The good news: CBS states its coatings are specifically designed to be hot worked, including flameworking, glass blowing, fusing, and beadmaking, and that the coating does not change the COE or integrity of the base glass. Dichro is torch-friendly material. It just has rules. Source: CBS FAQ.

The coated-side rule: cap it or burn it

The single most important habit in dichro flamework, repeated across manufacturer guidance and community archives, is this: the flame should only ever hit the clear glass side, never the coating. Direct flame on the exposed coating burns it off. In practice that means:

• Apply strips and pieces coated-side DOWN. When the coating faces the bead or gather and the uncoated backing glass faces the flame, the backing self-encases the coating against the work. Source: Lampwork Etc archive.
• Seal every edge. Edges are where dichro dies. If a strip’s edges are not tucked and sealed into the surrounding glass, the coating curls up at the boundary, oxidizes, and leaves a gray, frothy “scuzz” line. Experienced artists push clear glass over every edge of the strip before any further heating. Source: Lampwork Etc archive.
• Cap or encase for finished work. CBS recommends capping or encasing dichro with clear (or firing coated-side down against glass) to protect the coating during hot work. Capping has an aesthetic bonus: it magnifies depth, so the color appears to float inside the piece. Source: CBS FAQ.

Finding the coated side

Before any of that, you need to know which face carries the coating. The standard check is the reflection test: hold the glass at an angle over a dark background and touch the surface with a pointed object. On the coated side, the object meets its own reflection with no gap. On the uncoated side, the reflection is separated from the object by the thickness of the glass. Color running all the way to the edge when viewed at an angle also indicates the coated face. Source: Glass Tips.

Dichro formats at the torch: rod, sheet strips, and stringer

Dichro reaches the torch in several forms, and each has its own workflow.

Sheet strips are the common soft-glass route: thin dichro-coated sheet is cut into narrow strips, applied coated-side down onto the bead, edge-sealed, then capped. Some beadmakers pre-fire cut strips in a kiln (community recipes cite roughly 1300 F for around 20 minutes) to stabilize the coating and soften sharp edges before torch use; treat that as one artist’s forum recipe rather than a manufacturer spec. Source: Lampwork Etc archive.

Dichroic stringer for soft glass is typically made by encasing a dichro-wrapped or dichro-faced rod in clear before pulling. The coating is then already protected inside the stringer, and you can apply it like any other stringer without worrying about the flame side. If your stringer control is shaky, dichro stringer is unforgiving of overheating, so a small, precise flame from a torch like the GTT Cricket or a classic Nortel Minor is a comfortable match for this scale of work.

Coated boro rod and tubing feed implosion and pendant work: the dichro is gathered or laid onto a clear “canvas,” then worked so the coating ends up deep inside clear glass. The implosion pendant technique is essentially an encasement move performed in one gesture, and it is the reason dichro survives the sustained heat of pendant and marble work at all. Torches favored for inside-out and implosion work, such as the Nortel Red Max or GTT Lynx, give the pinpoint control this demands. Technique context: Corning Museum of Glass flameworking guide.

Encasing dichro so the sparkle survives

Encasement does two jobs at once. It is the protection layer that lets the coating live through repeated reheating, and it is the optical trick that makes dichro look like it is suspended in water. A clean clear layer over the coating deepens the color shift and keeps the interference layers away from flame, tools, and oxygen.

The craft challenge is doing it without trapping air. Every wrinkle, fold, or gap between the clear and the coated surface becomes a bubble, and bubbles over dichro read as dull spots. The techniques are the same as any encasement work: heat control, working from one side to push air out, and sealing edges before building up. Our guide to encasement without bubbles covers the mechanics in detail, and the glass pendant walkthrough shows where a dichro layer typically sits in a pendant build.

Why dichro burns off, crazes, or goes gray

Three distinct failure modes show up in dichro work, with three distinct causes:

• Burn-off. Direct flame on the exposed coating, or simply too much heat for too long, destroys the interference layers. Retailer summaries of manufacturer guidance and kiln-forum reports place the damage threshold at varying temperatures, so treat any specific number you read as approximate. The reliable rule is behavioral, not numeric: keep flame off the coating and keep exposed coating time short.
• Crazing. Overheated coating can crackle into a fine web. Note that crazed texture is not always damage: CBS sells a deliberately pre-crazed product line (“Crinklized” dichroic) where the crackle is the point. If you bought smooth dichro and it arrives at crazed, your heat did it. Source: CBS Crinklized.
• Gray scuzz lines. Unsealed edges curl, oxidize, and froth. This is the edge-sealing failure described above, and it is the most common beginner complaint.

Flame chemistry matters too. Experienced flameworkers consistently report that dichro “loves oxygen”: a cooler, strongly oxidizing flame is gentle on the coating, while a neutral or reducing flame burns it out much faster. This is practitioner consensus from community archives rather than a manufacturer spec, and it varies somewhat by coating color and brand, but it is widely repeated advice. If flame settings are new territory, start with our primer on neutral, oxidizing, and reducing flames. Source: Lampwork Etc archive.

Standard studio precautions apply when working or coldworking dichro: didymium or appropriate eyewear, active ventilation, and dust control when cutting or grinding coated glass. CBS markets the coating as inert, and no source we reviewed supports claims that the coating itself is toxic. As always, the manufacturer’s instructions for your glass, torch, and kiln take precedence over any general guidance here.

Buying COE-matched dichro (33 / 90 / 96 / 104)

Dichro is sold in COE-matched families, and matching is non-negotiable:

The compatibility lives in the substrate, not the coating. CBS coats compatible base glasses across these families, and the coating itself does not change the COE of the glass underneath. That also means the families are not interchangeable: dichro on a 90 substrate in a 104 bead is a COE mismatch and will crack like any other incompatible combination. Buy dichro explicitly labeled for the exact COE you work, from the same compatibility system as your base glass. Source: CBS FAQ.

Key takeaways

• Dichro’s color comes from dozens of ultra-thin metal-oxide layers and optical interference, not pigment, so the coating is the fragile, irreplaceable part.
• Cap it or burn it: flame touches only the uncoated glass side; apply pieces coated-side down, seal every edge, and encase in clear.
• Use the reflection test to find the coated side before you start.
• Formats differ: strips get applied and capped, stringer is usually pre-encased before pulling, and boro rod or tubing gets gathered and imploded so the coating ends up inside.
• Failures have causes: direct flame or excess heat burns off the coating, overheating crazes it, unsealed edges make gray scuzz, and a cool oxidizing flame is the community’s standard defense.
• Buy dichro labeled for your exact COE (33, 90, 96, or 104); the substrate determines compatibility and the families never mix.

Sources

• CBS Coatings by Sandberg, “Dichroic Glass FAQs”: https://cbs-dichroic.com/dichroic-glass-faqs/
• CBS Coatings by Sandberg, “Dichroic Glass Scratching”: https://cbs-dichroic.com/faq-items/dichroic-glass-scratching/
• CBS Coatings by Sandberg, “Crinklized Dichroic Coating”: https://cbs-dichroic.com/product/crinklized-dichroic-coating/
• Wikipedia, “Dichroic glass”: https://en.wikipedia.org/wiki/Dichroic_glass
• NASA Spinoff 2012, dichroic coating technology transfer: https://spinoff.nasa.gov/Spinoff2012/cg_2.html
• Lampwork Etc archive, dichro strip and edge-sealing thread: https://www.lampworketc.com/forums/archive/index.php/t-54881.html
• Lampwork Etc archive, coated-side and flame-chemistry thread: https://www.lampworketc.com/forums/archive/index.php/t-170197.html
• Glass Tips, “Dichroic coatings”: https://glasstips.blogspot.com/2018/08/dichroic-coatings.html

Editor’s note: temperature limits for dichroic coatings vary by source, with commonly circulated burn-off figures and kiln-forum crazing reports spanning a wide range, so this article gives behavioral rules instead of hard numbers. Flame-chemistry advice reflects experienced-artist consensus from community forums, not a manufacturer specification, and varies by coating color and brand. Always follow the glass and coating manufacturer’s guidance for your specific materials.