Strange silver DCG hologram

[whoiswei]

​Hi everyone,
​A friend of mine ran into a bizarre result while making DCG holograms recently: the final hologram came out completely silver-white, with no color dispersion at all.
​Formula used:
​Pure water: 84 mL
​Gelatin granules: 9.3 g
​5% Potassium Dichromate K2Cr2O7 solution: 16 mL
​Process: Mixed at a constant temperature of 42°C
​Because he was running extremely low on potassium dichromate, the dichromate concentration was severely under-dosed. Based on standard tuning and emulsion swelling calculations, we expected the replay wavelength to shift far into the infrared region and become invisible to the human eye. Surprisingly, it yielded a very crisp and bright silver hologram instead.
​His setup relies on a single light source: a Coherent OBIS LS 488-60 blue laser (488 nm, made in Singapore). No other lasers were involved.
​Has anyone encountered this before? What is the physical mechanism behind an under-sensitized DCG emulsion illuminated by a single 488 nm laser producing a broad-band silver/white hologram? Any technical insights would be greatly appreciated!

[Joe Farina]

I have used 12ml of 5% potassium dichromate with 6 grams gelatin (exposed at 488nm), and have not seen silver/white holograms. I doubt that the silver/white (a very broadband result?) was caused by the film formula. Rather, I think it's likely due to the processing or other factors. I was not able to view the photo, since my anti-virus software (Norton) blocked it for some reason. Your earlier photos of the coins did come through, however. There was some discussion a very long time ago by John Pecora about white DCG holograms. I will look for that thread. If I can find it, I will provide a link.

Update: I couldn't find the thread in which John described how he got a white DCG hologram, but the example he used was the angel hologram shown on the holowiki: https://holowiki.org/wiki/Main_Page As I recall, John used some kind of soaking step involving water (it must have been different from the usual water soak?) Maybe another forum member can find the post, or maybe other DCG people here can describe how it's done. I never got a really white (super-broadband) DCG hologram.

[whoiswei]

I have used 12ml of 5% potassium dichromate with 6 grams gelatin (exposed at 488nm), and have not seen silver/white holograms. I doubt that the silver/white (a very broadband result?) was caused by the film formula. Rather, I think it's likely due to the processing or other factors. I was not able to view the photo, since my anti-virus software (Norton) blocked it for some reason. Your earlier photos of the coins did come through, however. There was some discussion a very long time ago by John Pecora about white DCG holograms. I will look for that thread. If I can find it, I will provide a link.

Update: I couldn't find the thread in which John described how he got a white DCG hologram, but the example he used was the angel hologram shown on the holowiki: https://holowiki.org/wiki/Main_Page As I recall, John used some kind of soaking step involving water (it must have been different from the usual water soak?) Maybe another forum member can find the post, or maybe other DCG people here can describe how it's done. I never got a really white (super-broadband) DCG hologram.

I suspect both the formulation and the processing timing played a key role here. According to him, he followed a fairly standard DCG processing workflow: a diluted Kodak F-5 fixer bath, followed by a water rinse, and finally graded isopropyl alcohol (IPA) dehydration.
​This unique silver effect might be directly tied to that water rinse step. He mentioned leaving the plate in the pure water bath for a bit longer than usual, which could have induced excessive gelatin swelling. Additionally, his potassium dichromate was sourced from a titration standard solution—is it possible that standard-grade titration solutions contain specific stabilizers or additives that altered the matrix?
​Honestly, his silver result looks far superior to John's previous work, with virtually zero unwanted chromatic dispersion.
​(P.S. The previous post block was likely due to an issue with the image host, so I have re-uploaded the images via a different host.)

[whoiswei]

I have used 12ml of 5% potassium dichromate with 6 grams gelatin (exposed at 488nm), and have not seen silver/white holograms. I doubt that the silver/white (a very broadband result?) was caused by the film formula. Rather, I think it's likely due to the processing or other factors. I was not able to view the photo, since my anti-virus software (Norton) blocked it for some reason. Your earlier photos of the coins did come through, however. There was some discussion a very long time ago by John Pecora about white DCG holograms. I will look for that thread. If I can find it, I will provide a link.

Update: I couldn't find the thread in which John described how he got a white DCG hologram, but the example he used was the angel hologram shown on the holowiki: https://holowiki.org/wiki/Main_Page As I recall, John used some kind of soaking step involving water (it must have been different from the usual water soak?) Maybe another forum member can find the post, or maybe other DCG people here can describe how it's done. I never got a really white (super-broadband) DCG hologram.

It appears that this processing protocol is remarkably reproducible. He remade the batch strictly following the exact same formula, and the newly processed plates yielded identical, stunning silver-white results.
​What is most fascinating is that when tilting or rocking the plate, there is virtually zero spatial chromatic dispersion or rainbow color breakup. Instead, the entire hologram undergoes a uniform, monolithic spectral shift. This synchronized optical response across the whole field suggests an unexpectedly complex, super-broadband Bragg interference mechanism operating within the swollen gelatin structure.
​In terms of optical performance, this behavior almost mirrors supercontinuum generation in nonlinear fiber optics—where an intense pulsed laser beam propagating through a silica fiber broadens into a white-light coherent spectrum via complex nonlinear dynamics. Here, we seem to be witnessing an analogous spatial-domain phenomenon: a ultra-broadband reflection response that somehow maintains immaculate phase locking, spatial coherence, and image sharpness.

[whoiswei]

I have used 12ml of 5% potassium dichromate with 6 grams gelatin (exposed at 488nm), and have not seen silver/white holograms. I doubt that the silver/white (a very broadband result?) was caused by the film formula. Rather, I think it's likely due to the processing or other factors. I was not able to view the photo, since my anti-virus software (Norton) blocked it for some reason. Your earlier photos of the coins did come through, however. There was some discussion a very long time ago by John Pecora about white DCG holograms. I will look for that thread. If I can find it, I will provide a link.

Update: I couldn't find the thread in which John described how he got a white DCG hologram, but the example he used was the angel hologram shown on the holowiki: https://holowiki.org/wiki/Main_Page As I recall, John used some kind of soaking step involving water (it must have been different from the usual water soak?) Maybe another forum member can find the post, or maybe other DCG people here can describe how it's done. I never got a really white (super-broadband) DCG hologram.

你好，我发现论坛支持附件，不一定要图床，所以我把图片传到了附件

[holomaker]

Yes you need to do a warm water/soap bath before any alcohol baths

White Venus

IMG_1838.jpeg (1.96 MiB) Viewed 8458 times

[Din]

I think it's to do with emulsion thickness, or rather, emulsion thinness. Very thin emulsions produce very braodband images because the emulsion is too thin to take Bragg planes. Therefore, the result is just a surface hologram replaying in the Raman-Nath regime creating broadband images.

My initial explanation was that I was looking at burn-in, ie too much object and not enough reference. Then, it occurred to me that the splash of orange on the lower half and the lack of emulsion at the edges pointed to variations in the emulsion thickness. Joy concurred that it was an emulsion thickness issue.