Diazo (Speedball) gelatin hologram

Dichromated Gelatin.
Erik
Posts: 5
Joined: Mon Mar 01, 2021 11:06 am

Re: Diazo (Speedball) gelatin hologram

Post by Erik » Fri Oct 29, 2021 11:10 pm

Alright, two 10x12 (8x10 effective after edges are cut off) mold-coated sheets are in the refrigerator. I would usually make more for a weekend session but this is experimental, and I want my thick rain-X plates back to make regular DCGs for sale.

My 405 nm laser is a homemade ECDL which was operating well at the electronics bench, but became misaligned when bringing it into the laser room. Attempting to realign it was not immediately successful and I had limited time today so wanted to move on to making emulsion and plates. I also do not yet have a dichroic mirror for this wavelength yet (coming soon from ebay) to make it colinear with the other lasers and direct it through the same spatial filter. My table and especially the shutter depends on this so I want to complete it before using the 405.

I too suspect 405 is underrated for display work. My exposures in standard DCG with the 445 and 488 are easier to make bright gold than anything else, and this represents a rather large redshift from the recording wavelengths. It would seem that 405 would tend to produce great bright green replay under the same conditions. As we know, green is the most visible at equal power.
With that in mind, I have the 445, 488, and 568 all aligned and ready to go. The 445 is a commercial ECDL with an asymmetrical beam, but the other two are Sapphires and give excellent even (gaussian) exposure.
This brings me to a question I have had for a while - when beam exposures are quoted in mW/cm^2, how is this calculated with a beam intensity that is not uniform across the entire plate? Quote for a single point and measure the properties at that point in the finished hologram?

The emulsion and prep were as follows, largely following my typical DCG workflow:

11 g gelatin (Superclear 300 bloom, from Amazon)
80 mL DI H2O
Stir, soak until water is absorbed. Heat to 60 C with magnetic stirring. Keep beaker covered with new plastic sandwich bag to exclude dust.
Speedball diazo sensitizer - comes as a viscous dark liquid inside an empty-feeling bottle. Filled 3/4 full with DI water as per instructions.
Added 1.0 mL prepared diazo sensitizer. pH was almost unchanged upon addition of diazo sensitizer: 5.40 before, 5.35 after. Probably within the noise of my meter.
Added 1.0 mL of 1% safranin O - because the 405 was not going to be an option for this weekend, I wanted to have a higher chance of success. The absorption of safranin at 445 is relatively low, hopefully results will still allow some conclusions. pH still 5.35.
Turned off stirring to allow bubbles to rise
Cleaned 10x12 glass sheet with non scratch pad, hot water, and my favorite mix of laundry detergent, oxi-clean, and TSP. Rinsed with DI water, making sure the water break test passes. Applied two strips of tape to each long edge. Scotch transparent for one, Scotch "super hold" for the other. I prefer the "super hold" tape but nearly ran out on the first plate. ...think ahead next time...
Cleaned thick glass previously coated with rain-X following same procedure. Dried both sheets with microfiber cloth then wiped with lint-free cleanroom wipe.
Sheets into the (holography dedicated, filtered air) food dehydrator at 130 F. Loaded 20 mL emulsion into syringe.
Removed warmed plates, placed upon prepared paper towels on a level surface. Applied emulsion in a "T" pattern
Lowered upper plate (thick rain-X glass) onto lower (clean) plate. Allowed emulsion to fill the entire surface. Applied binder clips to the long edges.
Placed in (dedicated, non-food) refrigerator for overnight gelling. Stored diazo in the fridge as well.

I checked an aliquot of the emulsion after coating the first plate and noted it was fairly faintly colored. Added a second 1.0 mL of 1% safranin to the remaining emulsion and mold coated the second plate following the first. Plate 1 had the super-hold tape and so will be a thicker layer.

I used to add glycerol (around 1% of final volume) to my DCG emulsion but found I got much better storage if this was omitted. Plates would undergo quite a bit of dark reaction overnight, and be nearly unusable after two days dry at room temp, even in darkness. With so many possible variables, it's difficult to say this was certainly the cause but it seems likely at this point.

I work my regular job Tues-Sat but will have some time after work to demold, dry, and cut up the plates.
I'm thinking just making some plain gratings with each laser to begin with.

I will update with observations. Thanks for the collaboration, this is exciting!

Joe Farina
Posts: 720
Joined: Wed Jan 07, 2015 2:10 pm

Re: Diazo (Speedball) gelatin hologram

Post by Joe Farina » Sat Oct 30, 2021 5:46 am

Nice! Looking forward to your next report :)

Din
Posts: 330
Joined: Thu Mar 12, 2015 4:47 pm

Re: Diazo (Speedball) gelatin hologram

Post by Din » Sat Oct 30, 2021 8:58 am

Erik wrote:
Fri Oct 29, 2021 11:10 pm
This brings me to a question I have had for a while - when beam exposures are quoted in mW/cm^2, how is this calculated with a beam intensity that is not uniform across the entire plate? Quote for a single point and measure the properties at that point in the finished hologram?
The exposure is determined by an average over a range of points scattered over the illumination field, hoping that the variation in intensity is not too high. Remember also, the reference beam, being Gaussian, also has a variation. In the end, what's important is the ratio, as the reference beam intensity varies, so must the object beam vary. The ability to record with reasonable brightness (not efficiency) over a range of intensities is known as the dynamic range of the material. DCG has a fairly large dynamic range, while silver halide does not, compared to DCG.
Erik wrote:
Fri Oct 29, 2021 11:10 pm
Plates would undergo quite a bit of dark reaction overnight, and be nearly unusable after two days dry at room temp, even in darkness.
That sounds too fast. . Mostly, we were involved with HOEs, but, even with display pieces, We were able to keep plates for two or three weeks and still be use-able.

Erik wrote:
Fri Oct 29, 2021 11:10 pm
My exposures in standard DCG with the 445 and 488 are easier to make bright gold than anything else, and this represents a rather large redshift from the recording wavelengths.
The final colour of the display piece can be varied, from the recording wavelength, to about 100nm, its a balance between formula, recording and development; this is because of the high dynamic range of DCG. We were able to get some pieces below the recording wavelength.

Martin
Posts: 121
Joined: Sat Apr 04, 2015 2:36 am

Re: Diazo (Speedball) gelatin hologram

Post by Martin » Mon Nov 01, 2021 9:35 am

Erik wrote:
Fri Oct 29, 2021 11:10 pm
I too suspect 405 is underrated for display work. My exposures in standard DCG with the 445 and 488 are easier to make bright gold than anything else, and this represents a rather large redshift from the recording wavelengths. It would seem that 405 would tend to produce great bright green replay under the same conditions. As we know, green is the most visible at equal power.

That's interesting. I guess it largely depends on the specific type of gelatin. Exposing my kitchen gelatin at 405nm, I could easily make bright gold images with DCG and FEG (www.holographyforum.org/forum/viewtopic ... it=FEG+a_k). Particularly with FEG extremely broad banded holograms could be made, but relatively monochromatic red images as well.
With the diazo it looks somewhat different. The wavelength shift is much harder to control - though as of now I've seen anything from violet to red images with my gelatin. During the alcohol dehydration step the SPB gelatin seems to behave differently. At least with the layers coated on glass it sometimes appeared to be advantageous heating them exclusively from the rear side (with a hairdryer).

With that in mind, I have the 445, 488, and 568 all aligned and ready to go. The 445 is a commercial ECDL with an asymmetrical beam, but the other two are Sapphires and give excellent even (gaussian) exposure.
Wow, you must feel privileged! If you (or someone else) came across a reliable, not too expensive laser at 405nm or 445, I'd be happy to buy one.

Added 1.0 mL of 1% safranin O - because the 405 was not going to be an option for this weekend, I wanted to have a higher chance of success. The absorption of safranin at 445 is relatively low, hopefully results will still allow some conclusions. pH still 5.35.

At 445 or even 488nm you should easily get along without adding any dye.
Stored diazo in the fridge as well.
Good point, I forgot to mention. Under these conditions the SPB solution may keep a couple of months.
I used to add glycerol (around 1% of final volume) to my DCG emulsion but found I got much better storage if this was omitted. Plates would undergo quite a bit of dark reaction overnight, and be nearly unusable after two days dry at room temp, even in darkness. With so many possible variables, it's difficult to say this was certainly the cause but it seems likely at this point.
I agree. The reason for my opting for plasticizers like glycerol simply stems from my preference for film materials for most of my testing. Using film sheets definitely saved me a lot of time.
According to Kosar's book (Jaromir Kosar, Light-sensitive systems: Chemistry and Applications of Nonsilver-Halide Photographic Processes) most commercial diazo systems have some acid (e.g. oxalic acid, boric acid) added for improved stability. However, one can assume that SPB already contains some stabilizers most likely.

I'm thinking just making some plain gratings with each laser to begin with.
Yes, with a transmission grating, that's also where I used to start at with a new recording material. Well, actually, over the years it morphed into a combined method, allowing for the recording of both a reflection and transmission hologram at the same time: I put a glass plate on a coin. Then I add the recording sheet (glass or film). Next and on top of it I put a transmission grating. That "sandwich" structure is lit from a laser from above. So I'm simultaneously recording a contact copy of the transmission grating and a Denisyuk hologram of the coin.

Fantastic report, thank you, Erik!

Martin
Posts: 121
Joined: Sat Apr 04, 2015 2:36 am

Re: Diazo (Speedball) gelatin hologram

Post by Martin » Mon Nov 01, 2021 9:38 am

Din wrote:
Sat Oct 30, 2021 8:58 am

The final colour of the display piece can be varied, from the recording wavelength, to about 100nm, its a balance between formula, recording and development; this is because of the high dynamic range of DCG. We were able to get some pieces below the recording wavelength.
I was wondering about that 100nm shift. I would have expected more. What's the bloom strength of your gelatin?

Din
Posts: 330
Joined: Thu Mar 12, 2015 4:47 pm

Re: Diazo (Speedball) gelatin hologram

Post by Din » Tue Nov 02, 2021 8:46 am

Martin wrote:
Mon Nov 01, 2021 9:38 am
Din wrote:
Sat Oct 30, 2021 8:58 am

The final colour of the display piece can be varied, from the recording wavelength, to about 100nm, its a balance between formula, recording and development; this is because of the high dynamic range of DCG. We were able to get some pieces below the recording wavelength.
I was wondering about that 100nm shift. I would have expected more. What's the bloom strength of your gelatin?
For display work we used 250, for technical work we used 350. For display work, we rarely tried to control centre wavelength and bandwidth, letting it settle wherever it would (noting the difference between summer and winter). Mostly, we shot at 488 and it would settle to a golden yellow. Once, someone wanted a very narrow band green, so we shot at 514, and hardened/processed to get to about 520. For technical; work, we generally needed about a 10 - 20nm bandwidth right across the spectrum. We managed to get everything from 440 (using a 457nm laser) to about 780nm (using a 514 and geometry). Then, of course, there were our pseudo-colour DCG. Don Broadbent used to use a more granular form of gelatin, instead of a powder. The only advantage I saw was that it dissolved faster.
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Din
Posts: 330
Joined: Thu Mar 12, 2015 4:47 pm

Re: Diazo (Speedball) gelatin hologram

Post by Din » Tue Nov 02, 2021 10:06 am

Correction, Joy has just told me that we used 300 bloom for technical work, not 350.

Apropos of centre wavelength and bandwidth for technical work, below is a plot where the recording laser was an Argon at 488nm, the centre wavelength is about 490, and with a bandwidth of about 20nm.
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Martin
Posts: 121
Joined: Sat Apr 04, 2015 2:36 am

Re: Diazo (Speedball) gelatin hologram

Post by Martin » Thu Nov 04, 2021 2:55 am

Pretty amazing! Thanks for the info, Dinesh.

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