Can anyone ID these antique(?) colour filters?

[Iain P]

I bought a box of filters at an antique fair yesterday. The seller thought there were perhaps something to do with an optician, but I'm fairly sure they were used for photographic purposes. He thought they are late Victorian, but that's pure guesswork.
There are 13 in the box, with slots for 3 more, presumably missing.
They are made of thick glass, 1.5" square, with a coloured sheet of gelatin or similar material sandwiched between.
Some have a number etched into the top corner, and some have an additional L etched into the top left corner, and some have no markings at all. The colours range from deep cobalt blue, to a deep maroon, with rich oranges and greens along the way, but no yellow.
A puzzling feature of them is that they are all rather dark, with an exposure compensation of around 25X. This seems a very suspiciously high filter factor for Victorian / Edwardian photography!
If anyone has any ideas about what they are or how they would have been used, I'd love to hear!
The images are here on my blog. Thanks, Iain
https://fouragesofsand.blogspot.com/2021/11/puzzling-antique-glass-filters.html

 

[AgX]

What would have been the use of this set for photography in Victorian times? I do not see any.
(Well, it depends on the definition of "victorian")

 

[MattKing]

Someone might have re-purposed the case.
Could they be for darkroom printing an earlier version of variable contrast paper?

 

[Kino]

They appear to be lantern slides. Perhaps they were used as "mood" light coloring for stage shows.

I suggest you contact the Magic Lantern Society in the UK for possible identification;
http://www.magiclantern.org.uk/

 

[Nicholas Lindan]

These look like the light filters used by quacks for color light therapy. The best known of these quack devices was the Dinshah Spectro-Chrome. See https://en.wikipedia.org/wiki/Chromotherapy

 

[AgX]

One learns something every day at Apug.

 

[Iain P]

Thanks all, some interesting suggestions there.

What would have been the use of this set for photography in Victorian times? I do not see any.
(Well, it depends on the definition of "victorian")

They look quite similar to some of these here, from the early 1900s:
http://www.earlyphotography.co.uk/site/entry_M17-1.html

 

[Iain P]

They appear to be lantern slides. Perhaps they were used as "mood" light coloring for stage shows.

I suggest you contact the Magic Lantern Society in the UK for possible identification;
http://www.magiclantern.org.uk/

Done, thanks. I'll let you know what they say.

 

[AgX]

My point on "victorian" was that colour taking-filters make no sense as long as spectrally sensitized emulsion was not yet invented, or rather employed. A red filter in this context even only made sense the moment sensitisation for red was employed.

 

[BAC1967]

I like the magic lantern answer but they could also be microscope filters. There is a similar Boucher & Lomb set on eBay right now, search for item # 402722442519

 

[Iain P]

My point on "victorian" was that colour taking-filters make no sense as long as spectrally sensitized emulsion was not yet invented, or rather employed. A red filter in this context even only made sense the moment sensitisation for red was employed.

Good point. So they can't be for standard photographic purposes then, or at least must be much later.

 

[Petrochemist]

I wonder if the numbers corelate to the Kodak Wratten filters. The only one you show is a #7 which is missing from all the wratten lists I've seen. (one of only 20 numbers below 100 that are skipped in my compiled data) The blue one looks similar to a #47.
Many of these numbered filters also have a letter code.
The filters include many that are not intended for photographic use. (microscopy/printing/scientific...)
The system was in use prior to 1912 when it was sold to kodak, so would easily be old enough to tie in with a seller thinking they are Victorian/Edwardian...

If you list the codes & their corresponding colours I can check with my old Wratten handbook to see if they are consistent, & quote the intended use if present (listed for ~95%)

If you want to drop them round to Harwich I could also measure their spectra using the spectrometer at work & could compare the spectra with those in the handbook

 

[Iain P]

I wonder if the numbers corelate to the Kodak Wratten filters. The only one you show is a #7 which is missing from all the wratten lists I've seen. (one of only 20 numbers below 100 that are skipped in my compiled data) The blue one looks similar to a #47.
Many of these numbered filters also have a letter code.
The filters include many that are not intended for photographic use. (microscopy/printing/scientific...)
The system was in use prior to 1912 when it was sold to kodak, so would easily be old enough to tie in with a seller thinking they are Victorian/Edwardian...

If you list the codes & their corresponding colours I can check with my old Wratten handbook to see if they are consistent, & quote the intended use if present (listed for ~95%)

If you want to drop them round to Harwich I could also measure their spectra using the spectrometer at work & could compare the spectra with those in the handbook

Well that's fantastic! Thank you for the information and the kind offer. I'll scan the filters properly today and post the results here.
Iain

 

[Petrochemist]

Well that's fantastic! Thank you for the information and the kind offer. I'll scan the filters properly today and post the results here.
Iain

No problem - I collect data on filters for full spectrum photography
Scans wouldn't be any good for measuring the spectra scans are reduced to 3 or 4 colours (RGB or CMYK) while the spectrometer looks at each wavelength in turn to at least 5nm resolution (60 data points across the visual portion, but with UV & NIR available too).
I suspect typing will prove easier for listing the labels

 

[Bill Burk]

I like the magic lantern answer but they could also be microscope filters. There is a similar Boucher & Lomb set on eBay right now, search for item # 402722442519

This was my initial thought, contrast filters for lighting for microscopes

 

[Iain P]

No problem - I collect data on filters for full spectrum photography
Scans wouldn't be any good for measuring the spectra scans are reduced to 3 or 4 colours (RGB or CMYK) while the spectrometer looks at each wavelength in turn to at least 5nm resolution (60 data points across the visual portion, but with UV & NIR available too).
I suspect typing will prove easier for listing the labels

A proper evaluation with a spectrometer would be fascinating! I'll PM you about this now, but here are the scans anyway, just for general interest though even capturing them in RGB proved difficult and the results are sub-optimal...
Interestingly, after the suggestion that they might have been used in microscopy, I posted the blog link on a photomicroscopy forum and someone said: "Spectoscopy and colorimetry might have wanted comparison filters. Be interesting to pass a broad spectrum light through them and (if a friend has a spectrometer) see what passes through. On the odd chance they narrowly pass some range, could be they were part of a scientific instrument?"
The scans: https://fouragesofsand.blogspot.com/2021/11/follow-up-to-puzzling-antique-filters.html

 

[Petrochemist]

A proper evaluation with a spectrometer would be fascinating! I'll PM you about this now, but here are the scans anyway, just for general interest though even capturing them in RGB proved difficult and the results are sub-optimal...
Interestingly, after the suggestion that they might have been used in microscopy, I posted the blog link on a photomicroscopy forum and someone said: "Spectoscopy and colorimetry might have wanted comparison filters. Be interesting to pass a broad spectrum light through them and (if a friend has a spectrometer) see what passes through. On the odd chance they narrowly pass some range, could be they were part of a scientific instrument?"
The scans: https://fouragesofsand.blogspot.com/2021/11/follow-up-to-puzzling-antique-filters.html

The numbers are clearly not Wratten codes
1 is a UV, & 2,3, 4, & 6 are all shades of yellow.

I've taken the rest of the week of work in an attempt to use up some of my holiday (I've still got over 3 weeks before year end) but will have a look at the colours that are described as being for microscopy when I'm back. I think the range here is too widespread, I seem to remember a more varied assortment chosen to boost contrast of specific colours.

 

[250swb]

My point on "victorian" was that colour taking-filters make no sense as long as spectrally sensitized emulsion was not yet invented, or rather employed. A red filter in this context even only made sense the moment sensitisation for red was employed.

The filters could have been used in the Autochrome process for making colour photographs, this started in around 1895 so still within the Victorian era.

 

[AgX]

There was colour photography before the Autochrome plate, in spite of the obsession for Autochrome here at Apug. Good, commercially viable spectral sensitisation was achieved around the turn of the century.

 

[Bikerider]

Is it possible these may be filters to use with the original Ilford multigrade that was around either just before or after the war and were still in use around 1960/64 I started picture taking around 1962 bur had not graduated to printing my own and I got a friend at work to print a set off for me. I didn't ask him again because they were awful but the paper was clearly marked 'Ilford on the back and this friend told me they were printed using variable contrast paper.


Update

Ilford had a variable contrast paper first in 1930 but it was not a success. But I have no idea when it was discontinued. When I was searching Ilford for information I came across this about Ilford. It makes interesting reading.

https://www.gracesguide.co.uk/Ilford

 

[Bikerider]

I don't think they are 'lantern slides'. Lantern slides were normally 3.25" x 3.25" in size. Early ones had hand painted images easily identified by obvious brush strokes when projected. Later B&W silver based sensitive slides were sold in packs of 12. They were exposed by contact printing negatives, or when 35mm came along, by enlarging onto the sensitive surface. There were as far as I can find out, they never used colour emulsion.
I remember in 1963 there were some lantern slides, only 2"x 2"shown at my Photographic Society. Like the larger ones, they were on glass with the emulsion side covered over with a piece of plain glass which was bonded to the image plate using gummed paper strips. The actual sheer quality when the larger ones were projected, were breathtaking! Far far better than prints or slides and modern Projected Digital Images would not even have come close.

 

[250swb]

There was colour photography before the Autochrome plate, in spite of the obsession for Autochrome here at Apug. Good, commercially viable spectral sensitisation was achieved around the turn of the century.

Actually I was responding to what the filters could have been used for, not recounting the history of colour photography.

 

[Petrochemist]

The visual spectra of these filters is:

The best match I've seen among filter spectra so far suggests they are 'monochromats' but I can't currently find my Wratten handbook for a more detailed explanation.
All seem very dark & I can't help wondering if the lower transmission near the eyes maximum sensitivity (550nm) is deliberate.

Another Kodak handbook has the following about their monochromat set:

 

[Iain P]

The visual spectra of these filters is:
View attachment 291216

The best match I've seen among filter spectra so far suggests they are 'monochromats' but I can't currently find my Wratten handbook for a more detailed explanation.
All seem very dark & I can't help wondering if the lower transmission near the eyes maximum sensitivity (550nm) is deliberate.

Another Kodak handbook has the following about their monochromat set:
View attachment 291222

That's quick work there! Many thanks. I only posted them on Saturday ;-) . It's amazing to see the spectra there, even though my understanding is at a very low level...
Iain

 

[Petrochemist]

That's quick work there! Many thanks. I only posted them on Saturday ;-) . It's amazing to see the spectra there, even though my understanding is at a very low level...
Iain

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