These might be made by Holophane. I believe they produced a lot of the glass for early fluorescent fixtures.

I've got some diffuser lenses from some recessed fluorescent fixtures in a building built in 1949.  These fixtures were set in a hard plaster ceiling.  I'd like to know a probable manufacturer.  Anyone have an idea who might have produced these?  Photos attached.

No, the 1960s OV-15.

the OV-25 the one "left outside" from late 79?

I would have interest depending on the shipping price

https://www.youtube.com/watch?v=BtMqx5P74n4
In this video, Les' Lab makes an integrating sphere. His channel does a lot of optical stuff, mostly laser related. Therefore the integrating sphere he makes is very small, but he does reveal some excellent information.

Commercially, integrating spheres are internally coated with a special coating of mostly PTFE called Spectralon. Not very accessible, and even if you were able to buy it you would still be spending a heck of a lot of cash for it. But a coating made of PVA glue and barium sulfate apparently is a reasonable alternative. The paper that he cites claims a 95% reflectivity of the coating (as opposed to the >99% reflectivity of Spectralon). Barium sulfate is also apparently sufficiently non-fluorescent so it isn't gonna mess up spectrometer measurements. Obviously this is not quite as good as Spectralon, but with my non-existent optical expertise I conclude that it is probably good enough.

So far all of these things are easily accessible. The only remaining problem I see here is selecting a spherical container large enough for HID lamps. In the video he used a cannonball mold, but unsurprisingly they don't make them big enough for our purposes. All we need are two spun sheet metal hemispheres. You would think this would be easy but apparently not. So far I found these stainless hemispheres for decorating:
https://www.amazon.com/dp/B09ST7PY3H
You can find them bigger than 12" but they get really expensive, and 12" really isn't that big. Obviously not as expensive as an actual integrating sphere, but that isn't saying a lot. Anybody else have other ideas for enclosures?

Soon I will need to do something with my QL 114. It's in 250W HPS with the flat glass lens. I'm willing to trade it or sell it. Preferably I would not ship this as it would cost over $200 to ship. I want to let someone else have it for two reasons: 1, I think it would be nice if someone other than me could also have one of these, if anyone wants one, and 2, sometime in the spring or summer I will get the drop lens variant of this fixture, and I don't have room for two indoors. If I still have it by then, it will be moved outdoors and covered with a tarp, with all openings covered up with some tape. In the meantime I will clean this up. I will not be scrapping this fixture.

PM me any details if you want it.

Images:
https://www.lighting-gallery.net/gallery/displayimage.php?album=8994&pos=0&pid=262808
https://www.lighting-gallery.net/gallery/displayimage.php?album=8994&pos=1&pid=262776

Note: Does not come with lamp

Indeed base etching or stamping was often also done, but mainly for lower volume lamps made at slower speeds.  On the highest speed lines for GLS and FL lamps, glass etching was the most common.  In the 1990s some types of ink for inkjet printers were developed that had excellent initial adhesion - but being polymer based tended to fade during lamp life.

The light diffusion coating of good quality integrating spheres is actually surprisingly expensive.  It is typically made from barium sulphate with a reflectivity set to 80% - this material being used on account of its relatively flat spectral reflectivity as a function of both wavelength and wall temperature, and to ensure the necessary number of internal reflections for the integration principle to work correctly with light sources having different luminous intensity distributions.  Without that, it would be necessary to calibrate the sphere differently for different lamp types and power loadings (which is sometimes still done where greater precision is required).  At the last time I had to order some of this paint, its price was a little under €2000 per litre - as such, for many years most of the lamp companies used to manufacture this paint themselves in their own chemical labs.  I had to make it a couple of times during training in my earlier career, quite an interesting process!

If the sphere is large enough, a lamp explosion is usually not too problematic because only a very small percentage of the inner surface is damaged.  More of a problem are the shards of broken glass which have to be cleaned up each time.  The barium sulphate paint has very poor adhesion, and can be brushed away with light contact.  It is out of the question to clean the inside of the sphere with any kind of brush, so the pieces had to be picked up by hand or vacuumed away.

Re-calibration is pretty simple - just install the reference lamp, give it 30 minutes to stabilise, and then scan the reference spectrum again.  This is done every few days or weekly anyway, to monitor the stability of the sphere as ambient temperature and humidity vary, but then using a checking lamp rather than the actual calibration master.  Since air conditioning has become the norm in recent years, sometimes the spheres can run for months at at time without need for re-calibration.

@James
Thank you for all of that information! I had no idea that this would be a regulated thing with requirements.

Another alternative is to stamp them on the metal ends of the tube, or metal base of the bulb. I have seen laser etched labels on lamp bases as well. Well hopefully modern etches hold up well.