I have purple tinted lenses on my 1926 Ford touring, anybody know anything about these?
Thanks in advance & Happy motoring,
Warren, Lots has been written in the past. Type "purple lens mtfca" into Google and lots of topics from the past will pop up.
I have a set on my 22. The old glass contained an element which turned purple when exposed to the sun. Those are probably original lenses which have been parked in the sun for many years.
I have a set of those on my 26 Tudor as well. I believe the presence of manganese in the glass and long exposure to UV rays in sunlight is responsible for the discoloration. They do look cool, but i don't know if I would care to use them as headlight lenses for night driving at all.
There were some lenses that were sold purple (violet) as new accessories.
Most purple (sun colored amethyst, or s.c.a.) glass was produced
before WWI. It is unusual that post-war Ford lenses were made using
manganese, as Germany was the primary world supplier and they
stopped exporting it and used it in their high grade steel production.
This caused most U.S. mfr's. to go to selenium as a de-colorizing
agent for their glass. Selenium will cause glass to yellow when UV
exposed, but rarely very dark like some of the s.c.a. glass can get.
It was the iron oxides present in most silicas that caused glass to
naturally achieve an aqua color. Most people today would be familiar
with old fruit jars and pre-1910 patent medicines or telephone insulators
being made in these aqua shades. The users simply did not care if
the glass had color, and thusly did not wish to pay the extra production
cost for decolorizing agents. However, items like lamps, lenses, and
shades WERE expected to be clear, and the extra effort was made
Along with much more stringent batch production and heat times.
Oddly, a few major mfr's. somehow managed to come into large supplies
of manganese after the war and used it in their production. The T lenses
come to mind, as does a huge amount of Whitall Tatum's insulator
production around 1920-3. The glass mfg. industry is pretty tightly
knit and it would not surprise me to learn Tatum or a nearby firm
(Millville, NJ) made lenses for Ford and others during this period,
or perhaps even as an aftermarket parts supply source ???
... one more thing:
If the batchmaster was really on top of his game and added just the
right amount of manganese to counteract the iron oxide content, the
glass would chemically balance and remain crystal clear. It was only
when excessive manganese was added to the batch that it purpled
upon exposure to UV rays. Of course, the more in excess, the darker
it would purple.
A common misbelief about this process is that the longer the glass is
exposed to UV rays, the darker it will become. Most glass achieved it's
maximum depth of color within months of exposure, that depth being
determined by the chemical imbalance, not more exposure.
Thank you to all who took the time to respond with your answers. Special thanks to Chris and Burger, for their answers.
If you want to speed up the process you can us a special light bulb that will purple the glass in a few days. Years ago I built a wood box with a lid and put a light inside to purple old medicine bottles. The bulb was called a germicidal light and at the time I bought it at the local hardware store....I think, (its been at least 40 years ago). I still have it and keep thinking I will get it out and darken the lens from my TT. I kinda like the purple look, gives it a little patina. If you want to try this, read and follow any warning labels that may apply to the bulb.
Reread my post. Lenses will only purple to the level of chemical imbalance
present. Some lenses will reach a strong purple potency. Others will max out
at a light pink, no matter how much UV you throw at them.