Punty

CFL glass: color that depends on the light

CFL colors are borosilicate colors that look one way in daylight or under an incandescent bulb and another under fluorescent light. The name comes from compact fluorescent lamps. Northern Waters' rig here reads amber in warm light and moves toward violet-blue under fluorescent tubes.

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Where the name comes from

CFL stands for compact fluorescent lamp, the twisted fluorescent bulb. Glass Alchemy, one of the companies that make colored borosilicate rod, says its color Serum was "the original CFL-reactive color": champagne yellow in natural light, soft pink under a CFL. Glass Alchemy's Thomas Grimmett wrote in 2017 that when the color came out, "the term 'CFL' was not used by anyone in our industry to describe a color."

Other makers have their own. Northstar's Gemini, made with Gaffer Glass, is described as purple in natural light and light cobalt blue under a 2700K CFL. Trautman Art Glass describes its Phaze as bright magenta under fluorescent light and close to clear champagne otherwise, and collectors also call colors like these "shifty."

One rig under two kinds of light Two color swatches for the Northern Waters rig: amber gold under warm light, and violet-blue under fluorescent light, as its listing describes them. Warm light: amber gold Fluorescent light: violet-blue Northern Waters' rig, as its listing describes it
Color swatches drawn from the words in the listing, not taken from a photo. A photo only ever shows one kind of light.

Why the color moves

The color makers don't publish what's in their CFL colors. Glass science outside pipe making explains the effect in general terms.

Fluorescent lamps give off light in narrow bands rather than a smooth spread (a Corning patent puts the sharpest of them at about 545 and 620 nanometers), and some glasses absorb light in equally narrow bands. When the bands of the light and the bands of the glass line up differently, the same glass looks like a different color. Corning's patent describes a glass made with rare earths that looks pink under incandescent light and green under fluorescent light.

That explanation is about glass generally. We don't claim a particular ingredient for any color on this site.

What changes it

  • The bulb. Elev8 Glass Gallery notes that the glass reacts to fluorescent light generally, not only to compact bulbs, and that the color temperature of the bulb changes how far it moves; Northstar's description of Gemini names a 2700K CFL.
  • Thickness. Bullseye, which makes glass for fusing rather than for pipes, notes that its shift colors change with thickness as well as with the light.
  • Blacklight is something else. UV-reactive glass glows under ultraviolet light; nothing in the sources says CFL colors glow.

We don't say how any piece looks under LED bulbs, because no source covers it.

Seeing it in the photos

Every product photo is taken under one light, so a photo can't show the shift. Where a listing names both colors, the piece's page says so, as on Northern Waters' rig. If you want to know how a piece looks under a particular light before you buy, ask about it.

Where to look on the pieces here

  • Northern Waters' rig: the whole body and its faceted crystal clusters are CFL glass, amber in warm light and violet-blue under fluorescent light.
  • PHD Glass's Rip Curl bottle: listed as full CFL, yellow in the photos.
  • Whitney Harmon and Skar's collab: its two-tone color includes CFL reactive glass.

Sources

  1. Glass Alchemy, Serum, champagne yellow in natural light, soft pink under CFL; Glass Alchemy's claim that Serum is 'the original CFL-reactive color'
  2. Thomas Grimmett, CFL Potion, Glass Alchemy (2017), that 'CFL' wasn't used in the industry to describe a color at the time
  3. Elev8 Glass Gallery, What does CFL and Shifty mean? (2018), the glass reacts to fluorescent light generally; the shift depends on the bulb's color temperature
  4. ABR Imagery, Northstar Gemini rod, purple in natural light, light cobalt blue under a 2700K CFL
  5. ABR Imagery, Trautman Art Glass Phaze rod, bright magenta under fluorescent light, close to clear champagne otherwise
  6. Corning Inc., US patent 11,535,549 B2, Multichroic glasses with praseodymium and neodymium, fluorescent light's sharp emission bands, and glass that looks pink under incandescent and green under fluorescent
  7. Bullseye Glass, Light Neo Lavender Shift Tint, shift hues change with the light source and with thickness

CFL color in the pieces here

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