Can anyone ID these antique(?) colour filters?

Helge · Nov 17, 2021

Definitely not lanterna magica.
Twenties at the earliest tenths.
The finish, the flocking, the font etc. can’t possibly be nineteenth century.
It’s a style thing, and the evident level of mass manufacture points to early twentieth century.

What’s the room at the front and the back of the box? Can’t be just a buffer.

Cokin like filters for some kind of holder?

Iain P · Nov 17, 2021

Yes, the slot does look like a holder doesn't it? George Auckland at the Magic Lantern Society kindly responded to my enquiry ages ago, but I only just spotted his reply in my Spam box this evening, and he confirms that they are not lantern slides:

"Your slides are a bit of a mystery. At 1.5 inches square they are too
small to be normal lantern slides. Also the density is high implying a lot
of light. I have a couple of ideas.

1. They are samples for supplying glass for stained glass
windows,domestic,churches or commercial.

2. They are scientific glasses for viewing hot flames and incandescent
objects.

We have a member who is a glass artist. I will copy her into this email to
see if she can suggest anything."

Iain P · Nov 17, 2021

Petrochemist said:
They arrived Monday morning & the light was poor during Monday & Tuesday lunchtimes so I didn't have too many distractions.
I've got visitors at work the next couple of days so might not be able to get to the post office till the weekend.

It might help a little to share something I noted on the colours the average person perceives for which wavelengths:
Violet 390-455nm
Blue 455-492nm
Green 492-577nm
Yellow 577-597nm
Orange 597-622nm
Red 622-780nm

The colours shown in the spectra are only to identify different filters & do not reflect the visual appearance

Sensitivity at the extremes is very much lower & can vary significantly with age etc. Another source gave total sensitivity as 100x better at 550nm than at 400nm or 700nm...
Yet another source showing sensitivty of human rods & cones in the eye only covered the range 400-710nm closer to the normally quoted visual range. This showed blue cones being 10-20x more sensitive in the mid range than at either end, with green & red cones this went up to 200x but a much wider wavelength range was seen.

Sorry I didn't note the sources for this info, just logged it for my own reference at various points over the last 10 years. I'm a great one for hoarding data

As an amateur astronomer, I'm sadly very aware of the lack of sensitivity of the eye to the red end of the spectrum! Most emission nebulae are about 90% hydrogen, and H-alpha light has a wavelength of 656 nm, so the eye struggles to see it at all, even through large telescopes. The famous Horse Head nebula remained stubbornly invisible to me even through a half-metre diameter reflector scope with a H-a filter. Your data nicely explain why the view though the telescope of deep sky objects is mostly pale green /blue.

Petrochemist · Nov 17, 2021

Iain P said:
Yes, the slot does look like a holder doesn't it? George Auckland at the Magic Lantern Society kindly responded to my enquiry ages ago, but I only just spotted his reply in my Spam box this evening, and he confirms that they are not lantern slides:

"Your slides are a bit of a mystery. At 1.5 inches square they are too
small to be normal lantern slides. Also the density is high implying a lot
of light. I have a couple of ideas.

1. They are samples for supplying glass for stained glass
windows,domestic,churches or commercial.

2. They are scientific glasses for viewing hot flames and incandescent
objects.

We have a member who is a glass artist. I will copy her into this email to
see if she can suggest anything."

I can't believe they'd be samples for stained glass, there is clearly a film sandwiched between two glass plates.
The second option sounds highly plausible & would fit well with the very dark nature of the filters. Kodak books certainly refer to similar filters as for scientific use.

Petrochemist · Nov 23, 2021

I've finally tracked down my Kodak filters handbook which only adds a little on the monochromat set (which appears to be what these are)
'For isolating light of narrow wavelength bands, for the determination of colour absorption factors, colour sensitivity & similar data'

Can anyone ID these antique(?) colour filters?

Helge

Iain P

Iain P

Petrochemist

Petrochemist

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