MTFCA Forum

I managed to crack the flat glass lens on one of the E&J 333 acetylene headlights on my 1912 Flanders 20. I plan to take it to my local glass shop to have a new one made. Should I ask them to make the new one out of plain flat glass like the original, or would laminated glass work? I wonder how well laminated glass would hold up to the heat (I do light my headlights occasionally, but only for a few minutes for demonstrations).

My vote is plain flat glass. Laminated glass is thinner and may break easier. I would also be concerned about the heat and the laminate.

Your original flat glass lasted for 112 years. I would go with flat glass, it has proven durability.

how thick is the glass in your lamps ? Mine is only “single strength” - laminated safety is much thicker, I question whether the plastic sandwich could take the heat.

If your looking for something stronger
Tempered Glass:
It is a type of heat-resistant glass that has been treated at high temperatures to make it extra strong. This makes it safer and more durable than regular glass, as it can withstand impacts and other physical shocks without breaking. It’s also resistant to thermal shock, which means it can handle rapid temperature changes without damage.
Tempered glass usually comes in two varieties: annealed and heat-strengthened. Annealed can withstand temperatures up to 250°C (482°F), while heat-strengthened ones have a maximum temperature rating of 350°C (662°F). This makes it suitable for applications such as fireplace doors, stovetop covers, skylights, and windows in areas with extreme weather.
They are also scratch-resistant and can be designed to be non-reflective, making them a great choice for outdoor applications. Furthermore, since it is four times stronger than regular glass, this type is more resistant to breakage in the event of an accident or impact.

+1 on the tempered glass suggestion.

Dan, good advice. Tempered glass lenses would have to be custom made to order, then go through the tempering process.

Does anyone know how thick the original glass is ?
Mine is very thin. Certainly not plate glass which used to be 1/4” before glass became gauged in metric.

DanTreace wrote: ↑

Sun Mar 24, 2024 6:27 pm

Use plain plate glass, just like original. Easy to cut to a round circle.

Don't use tempered glass, you cannot cut it, the tempering will make the glass shatter.

Don't use laminate safety either the plastic film between the glass will cause reflections and will distort and craze with heat of the gas lamp burner

Cutting a nice circle out of glass is best left to people who cut glass for a living. My local stain glass shop cut me a lens with what they called "Lens Glass" was thicker than windowpane glass.

Tempered glass can only be cut by a professional (annealing the piece or with special laser cutters)
Laminated Glass well not to use for all the reasons Dan mentioned above.

Common glass thickness includes:
3/32″ thickness (2.4 mm) – used in picture frames, small insulated glass units, not temperable.
1/8″ thickness (3.2 mm) – small cabinet door panels, insulated units, picture frames and small table tops.
3/16″ thickness (4.8 mm) – larger cabinet door panels, single pane window, small mirrors.
1/4″ thickness (6.4 mm) – all general glass applications, such as table tops (as protective cover), insulated units, interior & exterior door lites, shelves, framed shower doors.
3/8″ thickness (9.5 mm) – framed & frameless shower doors and enclosures, shelves, table tops, glass walls and partitions.
1/2″ thickness (12.7 mm) – larger shower doors and enclosures, larger shelves, larger table tops, countertops, glass walls and partitions, hand railings.
3/4″ thickness (19.1 mm) – very large table tops, very large shelves, larger countertops, mall fronts, glass floors.
1″ thickness (25.4 mm) – glass flooring, stair treads, tables, glass furniture.

As I understand it, tempered glass is glass which has been cut to size first, before it goes through the tempering process. You could probably have a half dozen plain glass lenses cut for the price of having one tempered lens made, without the delay.

Allan from down under.

Allan, makes good sense !
Frank, thanks for the additional information !!

Anyone ? Anyone ? Bueller ?
Still like to know how thick the original glass was ?

I just measured my broken lens and it is 1/8 inch thick.

Borosilicate glass, sometimes known as Pyrex, will get it done, cuts good, your glass shop may have it. Dave in Bellingham

Mark -
Is it possible the break was not heat-related? Something may have hit the glass while driving, or the lamp door got into a bind when you opened and closed it to light it. Perhaps the front orifice plugged momentarily with a drop of water and the rear jet flared forward and cracked it. Or maybe it was just turned up a bit high?

I had a cracked lens in the lamp of a car I bought (old photos showed it had been cracked for at least 35 years with the previous owner) and upon inspection, the door was badly sprung and the crack followed the bow in the brass door.

Laminated glass would not be less likely to crack, just would contain all the pieces it it does, either way still broken. The mirrors are the difficult and expensive piece, flat glass can be sacrificed to the acetylene gods (if that was the cause). If you did want something that might survive an acetylene flame, your best bet might be fused quartz, but it is not necessary and would probably cost more than a new set of lights... In addition to the other good suggestions here, make sure the burners are tight (and pointed the correct way).

I would get what you had if the glass fit the rim properly
and was secure. I have John Brown 16's and a ring holds the
flat glass against the rim securely so the lens doesn't fall
out while you are lighting up and have the doors open.

Heat is not a problem for the front lens. Like you say, I'll
light them for a couple of minutes standing still just to show
how they work. Driving with the acetylene headlamps lit, the
bonnets don't get as hot as the radiator. However, I will turn them off
if I see I'm going to be standing still for more than 4-5 minutes.

Thanks everyone for the reply's! I'll go to the glass shop today and ask for plain flat glass, like the original.

CudaMan wrote: ↑

Sun Mar 24, 2024 8:35 pm

I just measured my broken lens and it is 1/8 inch thick.

Thanks Mark !

TMiller6 wrote: ↑

Sun Mar 24, 2024 4:13 pm

My vote is plain flat glass. Laminated glass is thinner and may break easier. I would also be concerned about the heat and the laminate.

That's what I was thinking as well - the glass on an acetylene light gets toasty, and I'd worry about the laminate between the sheets.

I had a local glass company make one out of some plate glass for the gas headlight on the bike, which they then beveled to match the original, and it turned out beautiful! I don't think I'd need to replace it again (I hope not!!), my only regret was they came up with zeros for a replacement reflector (all there but cracked)...

Update - my local glass company called and said they had the plate glass lens ready for pickup, they had a scrap piece of 1/8 inch thick plate glass that was large enough to make one lens. Price, including polishing the edges, was eight dollars, a bargain IMO! It fit perfectly.

I asked them to obtain another piece of glass and make two more lenses for spares at their convenience. The headlights are E&J 366, BTW.