Project Description:
Twenty four 4x5 inch, red sensitive glass plates exposed to test new Cobolt Flamenco 660nm 500mw laser.
Plate types tested: Agfa 10E75 NAH, Agfa 8E75 (NAH), Agfa 8E75HD (NAH), Ilford SP696T (NAH), HRT BB640 (NAH).
All plates ranging in age from about 20 to 45 years old.
Hologram test setup: H2 transfer camera, H1 was 15 year old 12x16, 8E75HD NAH ruby pulsed portrait master exposed at 694nm transferred to 4x5" H2 image area, 1:1, both H1RC & H2RB collimated.
The purpose of these hologram tests was to ascertain whether or not the 660nm laser wavelength, and, more specifically, the Cobolt Flamenco laser, is suitable for exposing legacy Agfa, Ilford, and HRT red sensitive silver halide hologram plates and film. The plates and film tested were all originally designed for use with 632.8nm, 640nm, and/or 694nm laser light. In summary, the answer is yes, 660nm works well for successful exposures of these legacy materials.
The surprise finding (to me) is that these very old materials have lost two to three orders of magnitude of sensitivity as they’ve aged. Although not included in this series of test exposures, similar legacy green sensitive materials from the same manufacturers have not lost much sensitivity. Since it’s possible to make good exposures on all the red sensitive materials tested, regardless of this loss of sensitivity, it seems possible that it’s the red sensitizing dye(s) used that have lost sensitivity.
Some holographers making optical display holograms and using red sensitive legacy materials, particularly the Agfa 8E75HD and Ilford SP696T & SP673, use 632.8nm HeNe lasers with a maximum output power of about 50mw.
Newer SLM DPSS lasers at 640nm are now available at output powers up to 500mw as well as the 500mw 660nm laser used for these tests. Manufacturer's spec sheets for their legacy red sensitive materials show that their materials are very sensitive at 660nm as well as the more typically used 632.8nm and 640nm.
A major difference in these two new lasers is that the 660nm units are about 60% of the cost of the 640nm units and the 660nm units have double the warranty.
Anecdotally, holographers have found these legacy red sensitive materials to be significantly less sensitive than when new. The reasons have been variously ascribed to fogging and dark reaction, etc. while stored. It is this holographer's opinion that the poor results obtained by others, with these much lower power lasers, may have simply been the result of insufficient exposure due to a large loss of red light sensitivity in the legacy materials. The possible proof of this is demonstrated by the good results obtained when these same materials were exposed to two to three orders of magnitude more exposure than was required when new.
I welcome constructive comments and criticisms.
Below is a link to an Excel spreadsheet with data on each of the 24 test exposures. I tried to upload it here directly but it's too large (all the photos) for the forum to accept. Please let me know if you have trouble accessing the link.
Please note that the numerous Excel spreadsheet explanatory cell notes and photos will not be visible unless you download the XLSX spreadsheet to a computer (not iPhone or iPad).
https://www.dropbox.com/scl/fi/thlco6vy ... 75fwd0i3gq
Using a 660nm laser to expose legacy AgX Agfa, Ilford, HRT (BB) plates
Re: Using a 660nm laser to expose legacy AgX Agfa, Ilford, HRT (BB) plates
Have you any idea why the red sensitive film decayed faster than the green sensitive ones? At one time I thought it may have been differences in grain size, but they all are spec'd at the same grain size. So, I'm inclined to agree it may be the dye. but, why does the red dye decay faster than the green dye. Could it be they react differently to temperature? That is, at the same temperature, one decays faster than the other?jrburns47 wrote: ↑Mon Mar 14, 2022 2:33 pm The surprise finding (to me) is that these very old materials have lost two to three orders of magnitude of sensitivity as they’ve aged. Although not included in this series of test exposures, similar legacy green sensitive materials from the same manufacturers have not lost much sensitivity. Since it’s possible to make good exposures on all the red sensitive materials tested, regardless of this loss of sensitivity, it seems possible that it’s the red sensitizing dye(s) used that have lost sensitivity.
At any rate, the way to test whether it is the dye that makes the difference between red and green dye is to expose them both to blue. Since all silver halide films are blue sensitive, you remove the dye factor from the equation.
Re: Using a 660nm laser to expose legacy AgX Agfa, Ilford, HRT (BB) plates
thanks Din, so if the dye because age or heat becomes bleached, why not just dye it again there by restoring the dyes ability to transfer energy to the silver? mm nice info
Re: Using a 660nm laser to expose legacy AgX Agfa, Ilford, HRT (BB) plates
Dinesh,
The point of testing the 660nm laser was that it’s a red laser to expose red sensitive legacy materials. You could be correct about trying a blue laser, assuming one has an appropriate blue laser with which to test. That’s a whole other technical rabbit hole to go down that takes me away from the direction I’m trying to go in - use the red sensitive materials to make good finished display holograms. There’s a sub infinite number of ways to NOT make finished holograms now. That’s certainly one of them.
Dannybee,
As far as re sensitizing a several decades old gelatin emulsion with fresh red dyes - that sounds like another interesting experimental rabbit hole to go down. Have you tried this yourself? After an interesting email back and forth with Mike Medora (BB plates), it sounds like red dyes are a whole interesting sub genre by themselves. John Wiltshire, co-author of an interesting book about optical display holography with Martin Richardson, turns out to be an expert in silver halide emulsion development for holography. It would be interesting to hear his take on this.
The point of testing the 660nm laser was that it’s a red laser to expose red sensitive legacy materials. You could be correct about trying a blue laser, assuming one has an appropriate blue laser with which to test. That’s a whole other technical rabbit hole to go down that takes me away from the direction I’m trying to go in - use the red sensitive materials to make good finished display holograms. There’s a sub infinite number of ways to NOT make finished holograms now. That’s certainly one of them.
Dannybee,
As far as re sensitizing a several decades old gelatin emulsion with fresh red dyes - that sounds like another interesting experimental rabbit hole to go down. Have you tried this yourself? After an interesting email back and forth with Mike Medora (BB plates), it sounds like red dyes are a whole interesting sub genre by themselves. John Wiltshire, co-author of an interesting book about optical display holography with Martin Richardson, turns out to be an expert in silver halide emulsion development for holography. It would be interesting to hear his take on this.
Re: Using a 660nm laser to expose legacy AgX Agfa, Ilford, HRT (BB) plates
I suppose you could. This was brought up recently. I think you'd have to choose your dye carefully; it must take in the laser wavelength and transfer some of the energy to the silver halide molecule, so the quantum efficiency of the dye at the laser wavelength determines the appropriate sensitivity.
Re: Using a 660nm laser to expose legacy AgX Agfa, Ilford, HRT (BB) plates
Hi Jody,
a few years ago I had exactly the opposite problem: red Agfas (more than 20 years old) worked perfectly, while the green ones were completely dead.
Petr
a few years ago I had exactly the opposite problem: red Agfas (more than 20 years old) worked perfectly, while the green ones were completely dead.
You don't need a SLM one for testing plate sensitivity. A blue pointer for a few USD will be enough.
Petr
Re: Using a 660nm laser to expose legacy AgX Agfa, Ilford, HRT (BB) plates
Petr's observation makes me think it could be caused by random events. If so, this could be due to double random walk ("drunkard's walk") events. This seems to indicate that dark reaction is (probably) the cause.
Re: Using a 660nm laser to expose legacy AgX Agfa, Ilford, HRT (BB) plates
Petr & Dinesh,
Definitely odd that you had the opposite experience with Agfa materials vis a vis red vs green & thanks for the suggestion re a cheap blue pointer.
Re the blue pointer, I’m old school in the sense that whether or not a plate can be exposed (or not) and turn dark in developer, the only proof to me is if it can record a hologram. I was almost ready to throw out my red sensitive Ilford early in these tests since I was literally getting nothing. It was only after realizing that maybe a comparably MUCH larger exposure might be necessary for the Ilford, based on my prior successful tests in the sequence with the Agfa 10E75, that I finally got a result.
Re your opposite experience red vs green decrease/loss of sensitivity, in my tests with the red sensitive materials, large loss of sensitivity held true, to a greater or lesser degree, across manufacturers, i.e., Agfa, Ilford, HRT BB.
If/when you have time, download the spreadsheet with data about the 24 test plates and open it in Excel on a computer.
Other users of 8E75HD have also told me of a noticeable, if undefined, loss of sensitivity.
Regardless, I agree that storage conditions probably have a significant effect on people’s varying experiences with these legacy materials.
Definitely odd that you had the opposite experience with Agfa materials vis a vis red vs green & thanks for the suggestion re a cheap blue pointer.
Re the blue pointer, I’m old school in the sense that whether or not a plate can be exposed (or not) and turn dark in developer, the only proof to me is if it can record a hologram. I was almost ready to throw out my red sensitive Ilford early in these tests since I was literally getting nothing. It was only after realizing that maybe a comparably MUCH larger exposure might be necessary for the Ilford, based on my prior successful tests in the sequence with the Agfa 10E75, that I finally got a result.
Re your opposite experience red vs green decrease/loss of sensitivity, in my tests with the red sensitive materials, large loss of sensitivity held true, to a greater or lesser degree, across manufacturers, i.e., Agfa, Ilford, HRT BB.
If/when you have time, download the spreadsheet with data about the 24 test plates and open it in Excel on a computer.
Other users of 8E75HD have also told me of a noticeable, if undefined, loss of sensitivity.
Regardless, I agree that storage conditions probably have a significant effect on people’s varying experiences with these legacy materials.
Re: Using a 660nm laser to expose legacy AgX Agfa, Ilford, HRT (BB) plates
Hi Jody
Have you tried exposing the old red sensitive plates to green laser light?
Obviously they don't have the correct dyes to be sensitive to green but given modern green lasers are fairly powerful I wonder if the emulsion would respond anyway?
And a similar thought.... Were you ever to experiment with adding dyes back in to the emulsion... it might be worth thinking about adding green dyes in to a plate that was originally sensitized to red, which would allow you to use the more powerful green lasers with those old red plates.
Have you tried exposing the old red sensitive plates to green laser light?
Obviously they don't have the correct dyes to be sensitive to green but given modern green lasers are fairly powerful I wonder if the emulsion would respond anyway?
And a similar thought.... Were you ever to experiment with adding dyes back in to the emulsion... it might be worth thinking about adding green dyes in to a plate that was originally sensitized to red, which would allow you to use the more powerful green lasers with those old red plates.
Re: Using a 660nm laser to expose legacy AgX Agfa, Ilford, HRT (BB) plates
John,
I think that the red emulsion would respond to green laser light because the sensitivity never actually goes to zero. But, the sensitivity falls quite a lot. Below, the sensitivity curve for 8e75, and you can see it does fall to zero at 500nm, but still has sensitivity at 514 ( Argon) or 532 (Yag). I also had a quick look at the sensitivity of Slavich's pfg-01; in that film, there's fall of about 2 orders of magnitude for green. So, if Jody is finding a loss of sensitivity to almost 5 orders of magnitude in red film for red lasers, I'd suspect that there's be a further loss of 2 orders of magnitude, or more, when using a green laser. This is assuming that the dyes have not decayed, or there is no dark reaction, in which case the fall in sensitivity may be even more. Therefore a powerful enough green laser would record on a red sensitized film. But, with a fall of several orders of magnitude, you'd need a very powerful green laser, or, a long exposure, with the associated stability issues.