A part number written in ordinary ink on a quartz heater tube is gone after the first hot cycle. A high temperature marking coating for quartz and glass has to survive the same heat as the part itself, and keep its color and grip while it does.
Q: What Is a High Temperature Marking Coating for Quartz and Glass?
A: A Single-Part Ceramic Coating Rated Well Above Ordinary Paint
It is an inorganic, pigmented coating applied to quartz or glass to mark, color-code, block light or reflect heat on parts that run hot. Incure’s Epo-Weld™ HTC grades for this job are single-part, room-temperature-cure coatings: every grade in the group lists a 24-hour cure at 77°F, with no oven step required.
The base grade, Epo-Weld™ HTC-6006, is a water-based, phosphate-bonded brown-black coating rated by Incure to 2,000°F. Most of the colored grades are rated to 1,500°F, and the white reflective grade to 1,600°F. Always plan to the rating of the specific grade you order, not the family’s highest figure.
Matching the Grade to the Job
The family splits by what the coating has to do on the part:
- Durable marking and coding: HTC-6006 (brown-black, 2,000°F) for halogen lamps and quartz heaters.
- Heavier film build: HTC-6007 (brown-black, 2,000°F) is the high-viscosity version, at 4,000–6,000 cps versus 1,500–2,500 cps for HTC-6006, for thicker coverage and opacity on high-intensity lamps.
- Light blocking: HTC-6013 (jet black, 1,500°F) is a high-opacity barrier for masking lighting components.
- Color coding: HTC-6022 (cobalt blue), HTC-6031 (gray), HTC-6059 (light green) and HTC-6060 (dark green), all rated to 1,500°F, for sorting and identifying parts by color.
- Reflecting heat and light: HTC-6068 (matte silver) and HTC-6069 (off-white), rated to 1,500°F, plus HTC-6070, a glass-ceramic-filled white rated to 1,600°F for infrared heaters and UV curing lamps.
What the Numbers Say About Toughness
Most of the colored grades share one mechanical profile in Incure’s catalog: Shore D85 hardness, 11,500 PSI flexural strength and 2,300 PSI tensile shear strength. That consistency is useful. A plant can run several colors for coding without re-qualifying adhesion and hardness for each one, because only the pigment and the temperature rating change.
HTC-6070 is the exception. Its glass-ceramic filler gives a slightly softer D82 surface and 8,000 PSI flexural strength, with a higher 2,400 PSI tensile shear figure and a lower 1,000–2,000 cps viscosity. Treat it as its own grade during qualification rather than as another color of HTC-6006.
Email Us with your part material, peak surface temperature and what the coating needs to do (mark, block light or reflect) to confirm the right HTC grade.
Preparing Quartz and Glass for a Coating That Lasts
Phosphate-bonded and glass-ceramic coatings rely on a clean, oil-free surface. Fingerprints and handling oils on quartz leave a film the coating cannot bond through, and those spots are where peeling starts after thermal cycling. Clean and dry the surface first, then handle the part only by uncoated areas until the coating has cured.
Film thickness matters as much as cleanliness. A heavy single coat on a smooth quartz surface is more likely to crack during heat-up than a controlled, even film. For a darker or more opaque mark, HTC-6007’s higher viscosity builds thickness in fewer passes; on lower-viscosity grades, build thickness with thin coats.
Let the full 24-hour room-temperature cure finish before the first heat cycle. Bringing a partly cured water-based coating straight up to temperature drives off water too quickly and invites blistering. The same staged-heat logic applies to other high-temperature systems, as covered in Incure’s guide to bonding quartz and fused silica with high-temperature epoxy.
Where These Coatings Are Used
- Lamp manufacturing: marking halogen and high-intensity lamp envelopes, and blocking stray light from end caps.
- Quartz heaters and infrared emitters: identification marks plus reflective backing (HTC-6070, HTC-6068, HTC-6069) to direct radiant output.
- UV curing lamps: reflective white coatings that keep output pointed at the work.
- Laboratory and semiconductor glassware: color-coded marks (HTC-6022, HTC-6013) that stay legible through repeated heating.
Choosing Between This Family and Incure’s Other Glass Coatings
These marking and reflective grades are one part of a wider line. Incure’s overview of Epo-Weld™ high temperature glass coatings by function and substrate covers the rest of the HTC page: graphite protection, casting release and refractory sealing. For decorative or appliance-grade glass enamel on metal rather than quartz, the separate Epo-Weld™ HTGC high temperature coatings are the better starting point.
Final Thoughts
A high temperature marking coating for quartz and glass is chosen by three questions: how hot the part runs, what the coating has to do, and how thick it must be. Incure’s Epo-Weld™ HTC grades answer all three, with brown-black marking to 2,000°F, a full color range to 1,500°F and reflective whites to 1,600°F. Contact Our Team to match a grade to your parts and process.
Visit www.incurelab.com for more information.