Undated
Fenton
Fenton name in an oval: a maker clue for matching a pattern or colour, rather than a uranium-content mark.
Read the stamp
How to identify uranium glass
Uranium glass typically fluoresces a strong, bright green under ultraviolet light; examine the glass in a darkened setting and compare its colour in ordinary light. Manganese can give a weaker greenish-yellow response and lead an icy blue, so the colour of the glow matters.
Start with the glass in ordinary light
Uranium compounds can colour glass yellow, yellow-green or amber, and uranium also occurs in opaque types such as custard and Burmese glass. Transparent yellow to yellow-green material is often called Vaseline glass. Uranium glass is the broader description: not every uranium-containing composition looks like that transparent yellow type. Equally, other colorants can produce a similar daylight colour. Record the object’s normal appearance before comparing its response to ultraviolet light.
Look for bright green fluorescence
In a darkened setting, direct the UV light onto the glass and observe the body of the object. Uranium usually gives a vivid bright-green response. Reflected purple light from the lamp is different: it is the colour of the light source on the surface, rather than the characteristic emission from the glass. Compare more than one area of the piece and keep the same lamp and viewing conditions when checking two objects. Lamp wavelength and intensity affect how strongly a glass fluoresces.
Separate uranium, manganese and lead responses
Manganese can give a lemonade-like greenish-yellow fluorescence, often weaker than uranium’s bright green. It was also used to decolourise glass, so otherwise clear glass can show that response. Lead typically gives an icy-blue fluorescence; antimony can produce a weaker blue-white. The ingredients, their concentrations and the lamp all affect the result, and different ingredients can mask one another. A faint greenish glow in colourless glass therefore needs a different reading from a strong green uranium response.
Use maker marks for the next identification step
After identifying the material, inspect the base for a moulded name, letter, symbol or surviving label. Fenton and Boyd made uranium glass among other wares, so their marks can help locate a shape, pattern or colour name. The same companies also made other glass compositions: a Fenton oval or Boyd B identifies a maker, not uranium by itself. Compare the complete object, moulded decoration and mark with other examples of the pattern.
What the glow can and cannot date
Uranium glass was produced over a long period, including later decorative production, so a bright response does not assign an antique year. Date the maker’s mark and pattern separately. Some uranium-bearing compositions show little or no fluorescence, while a strong response does not state the uranium percentage. Keep visible colour, fluorescence and manufacturer identification as separate observations. Vaseline branding on a petroleum-jelly jar is a product name; it is unrelated to the glass collector’s colour term.
Examples
From 1998
Boyd's Crystal Art Glass
Boyd B in a diamond: identify the maker separately from testing a particular glass colour’s UV response.
Frequently asked questions
How do you identify uranium glass?
Look for its characteristic strong bright-green fluorescence under UV, compare the normal colour, and identify the maker and pattern separately.
Does all green-glowing glass contain uranium?
Manganese can produce a weaker greenish-yellow response, including in colourless glass. The glow’s colour and strength need to be read with the ordinary-light appearance and lamp conditions.
Is Vaseline glass the same as uranium glass?
Vaseline glass generally means transparent yellow or yellow-green uranium glass. Uranium glass also includes other colours and opaque compositions.
Can uranium glass be identified by its maker mark?
A maker mark helps identify the manufacturer and pattern. It does not specify uranium content, since makers used different glass compositions.