I'm So Blue

[Dutchelm05]

Happy Easter all,
Here is my first real attempt using my new MG 457nm laser.
It is a very different animal than my C532.
As you can see here is a tremendous amount of scatter.
Here are the stats
12-2.5-100
200mw of blue light
Mold process (4 hours old)
20 seconds exposure
40sec Fixer
4 minutes rinse
15 second in IPAs each (70/30, 30/70 and 91%)(90F)
100% IPA (100F) for 2 minutes
5 minutes blow dry

I am guessing either I am over exposing (although I tryed 10 seconds and 30 seconds) Or too much AmDi
The first one is the shot.
The second is showing all of the wonderful scatter.


Oh one last comment, When they first came out of the the 100% IPA to the blow dryer, the first few seconds it was a brillant red/orange, then shifted to green. I don't know if that is a clue or not.

Any ideas?
Thank you for your comments.
Tony

[Joe Farina]

Hey Tony, nice hologram, looks bright. When I think of "scatter," I usually have grains of silver halide in mind. It would be interesting if someone like Ed or Bob could give us a tutorial as to exactly what scatter is, and how it shows up in a hologram. I just think of it as light bouncing around excessively amongst small particles, but I don't have a clear idea about the holographic result. Maybe it would be a very light overall haze or fog. Then again, maybe there are other forms of scattering (as defined by holographers). I suppose scattering could occur during either recording or reconstruction. One of the attractions of DCG is its "grainless" nature, and I guess this is why you don't hear much about scattering in DCG. Not to say that scattering doesn't exist in DCG, but I haven't really heard anything about it. But if what you're seeing really is scattering due to small particles, then I have a comment (hopefully not a useless one).

I've wondered about the state of the dissolved dichromate, when it's added dry to the gelatin/water. Since gelatin is such an effective protective colloid, I wonder if it's possible that very tiny "clumps" are formed that don't fully dissolve. It may visually look dissolved of course, but blue scattering can occur with some very tiny particles, say for example 10nm. So I guess it would be important to get the dichromate dissolved all the way down to the molecular level. If Jeff Blyth is reading this, maybe he can shed some light on the issue. Personally, I thoroughly mix (with magnetic stirring) my dichromate in a small separate beaker with enough water to get it in solution, THEN I pour this into the heated gelatin/water and continue stirring. I haven't done any side-by-side tests to prove the usefulness of this, but since it's so simple, I just make it part of my routine.

Also, Tony, I would decrease the dichromate concentration for blue light, I would suggest trying Danny's formula or mine. By the way, did you notice any brightness increase when using blue instead of green?

[Dutchelm05]

Thanks Joe for the reply.
Yes, you are right, in that scattering may not be the best term to discribe this.
Perhaps the gurus can provide the right term (where are those guys by the way )

I have not changed my process as far as I know regarding mixing of the DCG from using 532nm to blue. I have to say I have never seen this while working in green. I do like your idea of mixing the AmDi in a water solution before adding it to the gel.

Also, Tony, I would decrease the dichromate concentration for blue light, I would suggest trying Danny's formula or mine.

My hope for this session was to make the same film as I did with the green laser. In John's paper he uses 3-12-100 and that worked well with green. I beleive he uses 488nm and has some great results. Perhaps next session I can try some lower concentrations.

By the way, did you notice any brightness increase when using blue instead of green?

It is hard to say at this point Joe. When I first started blow drying, the plate was a very bright vivid red/orange then shifted to green in about a minute. I have to say at first my heart was racing when I first saw it, then my excitement was dashed as it faded to green

I plan to try again Friday.

Colin, if we figure out what is wrong with this hologram, I can send it to you (or use this photo) for the trobleshooting section.

[Joe Farina]

Tony, it looks like you're getting shrinkage in the final result when your hologram goes from red to green. I would suggest using more gelatin and less water. As you know, I used Rallison's formula for "red" holograms with a blue laser: 3-30-200. So, in addition to reducing your dichromate content (and mixing it separately), I would add more gelatin. In the batches I've done thus far, I get red (but unfortunately rather dim) holograms when the emulsion is young, then they get brighter as the coated emulsion continues to age. I get optimal results when the coated plates are refrigerated for a 3-week period (I don't know why).

If you're planning to do 2-color work with 457 and 532, then it might be worthwhile to optimize results for each individual wavelength at first. Then, you could "average" the formula for work with 457/532 at the same time.

[Dutchelm05]

Thanks Joe, it looks like it is not a plug a play situation with the two wavelengths.
I thought in reading John's results it would be about the same formula for both wavelengths.
I will try again on Friday and try a few variations in AmDi concentrations and perhaps gelatin amounts.

I get optimal results when the coated plates are refrigerated for a 3-week period (I don't know why).

This is counter to everything I have seen and read, but I guess you would get less shinkage with harder gel?
In Danny's DCG 101 it used 2-2.5% AmDi but maybe that was with green.
His recent work was a no fixer process using blue and 1% AmDi
Back to the drawing board
Peace
Tony

[Dutchelm05]

Thanks Joe, it looks like it is not a plug a play situation with the two wavelengths.
I thought in reading John's results it would be about the same formula for both wavelengths.
I will try again on Friday and try a few variations in AmDi concentrations and perhaps gelatin amounts.

I get optimal results when the coated plates are refrigerated for a 3-week period (I don't know why).

This is counter to everything I have seen and read, but I guess you would get less shinkage with harder gel?
In Danny's DCG 101 it used 2-2.5% AmDi but maybe that was with green.
His recent work was a no fixer process using blue and 1% AmDi
Back to the drawing board
Peace
Tony

[Danny Bee]

wow tony... very nice first try

From looking at your data and your hologram...the plates have too much water in it. in other words they were not aged enough ... rember as they age they will shift a bit.... so I do think with more age the chrome need to be a bit lower let’s say 2g....for a bright yellow.
..Also this will allow more light to go through the plate.

Even blue light 457nm the plate need some overall hardness whether its ( light, heat ,age or fixer)

Depending on the overall hardness will determine water soak time. I have found that your overall hardness needs to be just enough to clear the exposed areas…and milkyness in the no-exposed areas.

It looks like there was good cross linking
What was the angle?

In casting the amount of water & gel controls the thickness, I was able to cast 7microns using 7-100 ...... I did try a dcg at that thickness it came out very broadband white image...
So what I’m saying here is, as you upper the amount gel per water... you narrow the bandwidth replay.

So let’s recap here.
Assuming that your process remains constant here are some variables
1: the amount of dichromate in the mix will center your replay bandwidth
2: the amount of gel per 100ml, 10 to 30 will determined your bandwidth
3: the overall hardness will determined your clarity and brightness and soak times

[Dutchelm05]

Thanks for the observations Danny

From looking at your data and your hologram...the plates have too much water in it.

So what do you think is the overall blue "scatter" (lack of a better work for now)?

I plan to use your black tape technique next time, I wish I remembered it last time. This way I can verify the correct exposure.

Tonight if I get the lighting figured out I will photograph some plates that have an odd characteristic. Some plates have something that looks like drips that all have the same orientation. It's odd.

What was the angle?

I am pretty sure I am at Brewster (give or take a degree). Could this cause something?

So let’s recap here.
Assuming that your process remains constant here are some variables
1: the amount of dichromate in the mix will center your replay bandwidth
2: the amount of gel per 100ml, 10 to 30 will determined your bandwidth
3: the overall hardness will determined your clarity and brightness and soak times

This is excellent information, thanks!
Tony

[Joe Farina]

I will try again on Friday and try a few variations in AmDi concentrations and perhaps gelatin amounts.

Tony, I forgot to mention that some people have had trouble with certain gelatin concentrations when using the mold-coating method, so maybe you should check with Danny about this first.

Regarding the concept of "scatter" with DCG, I think it usually refers to an overdone broadband hologram which is milky and bright. So the noise or scatter would be present in the reconstruction stage, and would result from the milky stuff, whatever that is.

Also, regarding the optimum characteristics of 3-week old emulsion, this was stated once (but only once, as far as I know) in an old paper by Schlesinger/Unterseher: "Dichromated gelatin holograms: a reliable method" page 81:

"The emulsion is best refrigerated for storage and then warmed just prior to use. Refrigerated material will keep for 2 to 3 months. A dark reaction takes place in the emulsion and the mixture will gradually harden. We found results to be ideal when the mixture was about 3 weeks old and other parameters were held constant."

Even though my plates had been aged after being coated on glass, I found good agreement in my tests to the above statement. Actually I think it's pretty well know that aged emulsion produces better results, and as I recall, this was also stated by John (the emulsion prior to coating in John's case). But it seems that the same effect occurs even if we're talking about already-coated plates.

[Dutchelm05]

Tony, I forgot to mention that some people have had trouble with certain gelatin concentrations when using the mold-coating method, so maybe you should check with Danny about this first.

I know some months ago I post some photos showing in higher concentrations of AmDi, the film crazed. Dave and others concurred it was most likely due to AmDi saturation (coming out of solution). That was in the 5-7% range. I think I may stick around the 1-3% area for now.

Regarding the concept of "scatter" with DCG, I think it usually refers to an overdone broadband hologram which is milky and bright. So the noise or scatter would be present in the reconstruction stage, and would result from the milky stuff, whatever that is.

Yes this sounds like a correct definition. I don't know what term to use for my issue.

Even though my plates had been aged after being coated on glass, I found good agreement in my tests to the above statement. Actually I think it's pretty well know that aged emulsion produces better results, and as I recall, this was also stated by John (the emulsion prior to coating in John's case). But it seems that the same effect occurs even if we're talking about already-coated plates.

I guess this is an area of debate, I've seen post and papers (Rallison) that state fresh is better. I do know that when I leave emulsion in the frig for a few weeks, it get browner in color. Not sure what it means however.

Thanks for all your great input Joe