Can anybody tell me why some headlight lenses have a pale amber cast? Were they manufactured that way? Just curious. Thanks
When exposed to sunlight, some pieces of clear glass will gradually turn purple. Others, however, will remain clear. What causes some glass to turn purple? The answer lies in the presence of a little-known element: manganese.
Thank you Richard. I meant purple rather than amber. Very interesting, and I suppose reproduction lenses stay clear?
Manganese was phased out as a flux in most glass production by the 1920s. That's why it's "antique" glass that turns purple. UV exposure causes the color to develop.
The purple Ford headlight and sidelight lenses that you see are most likely from junk cars/lamps that have sat outside and been exposed to sunlight daily for years.
(Message edited by Erik_johnson on January 03, 2017)
The purple will fade over time if not exposed to sunlight.
Wow, ... a lot of misinformation here.
Manganese was used as a decolorizing agent in glass production.
It neutralizes iron oxides, the most prevelent color-inducing contaminant
present in raw glass making materials (which, just to be thorough
in the response, produces the greens, blues, and aquas so familiar
in old bottle glass).
What causes purpling of the glass is an overdosing of a given glass
batch that exceeds the iron oxides present. The glass will come out
of production a grey-to-yellow tone when new, but upon exposure to
the UV rays of sunlight, with turn pinkish and then purple, ... key point
here: depending on the level of chemical imbalance of the manganese
Manganese-decolorized glass will turn to its full purple potential within
a year of constant UV exposure. It is not a matter of the more sun you
give it, the darker it gets. It will only get as dark as the chemicals present
will allow it to. The color will not reverse itself unless the glass is heated
to about 1000ºf.
Manganese is used in the production of high strength alloy steels, and
demand came to the fore about the time the Model T was introduced,
driving prices higher and causing glass mfr's. to seek out cheaper ways
to decolorize their glass. Selenium was one such chemical. It also has
a UV reaction, but turns the glass a light amber or "peachy" color. The
use of selenium was shortlived and soon methods to make very clear
glass cheaply were developed and the interesting colors ceased to be
part of glass mfg.
Good info there, thanks for the input, Burger ! I reckon your study of glass insulators led you to research many aspects of glass-making ?
Makes more sense that manganese had to do with color control, rather than being used as a flux.
Thanks, Rich. Yes, insulator study has proven a wealth of intel for all
sorts of things I never expected.
Incidentally, pressed glass of the type our lenses are made works best
at a temperature right around 2000-2200 degrees. To bring raw materials
to a point of flux requires a temp of around 3000º. The best fluxing agent
to reduce that heat level is glass itself. Just toss in a broken chunk of
something from the shop floor and the raw materials will melt at a temp
closer to 2000, cutting fuel costs and time by nearly 50%.
The glass industry calls broken glass shards "cullet" and it is a valuable
commodity in the production of new glass for the above reason.
Thanks one and all!! What would I do without this forum???
I have a set of Ford H lenses that have not seen sunlight in 25 years and they are very purple indeed.
The California Glass Works operated from 1912 to 1916 in Long Beach, California.
They made about a dozen different styles of insulators. Most of their glass was "flint
glass", ... the decolorized stuff that turns some shade of smoke or purple. Items
never exposed to the sun can be found in pretty shades of yellow to peachy-orange
and command 10x the price of the typical purple unit. As a result, some people have
experimented around with heating the glass back up to a point to reverse the chemical
reaction of the purpling. It can be done, but heating thick glass offers serious challenges
in keeping the glass from frscturing, due to thermal differences from the surface to inner
glass. Too much heat and the glass distorts or sags.
Trying to reverse the color change on T lenses would make no sense, but for some
insulator dealers/collectors, it is worth the gamble.
A variety of colors can be found in these CD 133 Californias. Note the stronger purple
swirls in some. This is caused by uneven mixing of the glass batch prior to pressing.
Here is an example of a Hemingray where the manganese was not thoroughly mixed
into the batch, resulting in swirls of purple in an otherwise decolorized insulator.
I was looking for some information on the "Smith Lens" headlights on my car and came across this old thread. There is a 1924 ad for the lenses on my car, but there also are period ads for violet lenses. (also by Smith) Apparently some lenses were tinted when new.