"Reflection display holograms on DCG"

[Joe Farina]

Here is a short but interesting paper on DCG with some unusual processing methods.

[Steven]

Thanks for that Joe.

I wonder why they include ammonium nitrate in their emulsion?

I have seen uneven marks on some of my earlier plates after processing using IPA baths that were above ambient temperature.
Initially I came to the conclusion that the marks, which were green and narrow band were due extra hardness (uneven swelling) in that area of the emulsion.
The wavelike pattens did change their position on reprocessing, so my processing procedure had something to do with it.

A few weeks ago I changed my processing procedure and since then, I have not seen these dreaded green wave like streaks on my holograms. My procedure:
After water rinse to wash out rapid fix, I place the plate in the swelling water bath at ambient temperature.
I raise swelling bath water temperature to target temperature, agitating continuously. I do this by floating a photo developing tray in very hot water, so that the temperature rises slowly. I then remove the developing tray from the hot water and allow the temperature of the swelling bath to decrease to the same temperature of my first IPA bath, only then is the plate removed from the swelling bath and plunged into the first IPA bath. I agitate rapidly for the first thirty seconds while the plate is in the IPA baths, except the last 100% IPA bath as its usually at 64C, and my fingers can only take about nine seconds in that.
I have also found that not having a sufficiently high temperature swelling bath increased the likelihood of me getting wavelike green pattens in the hologram.
I have increased the volume of liquid in each of my IPA baths to at least one litre, I think this tends to help too.

Steven.

[Joe Farina]

Hi Steven,

This may have nothing to do with the unevenness problem you mentioned, but just in case, I'm attaching a paper. As I recall, you're using a dip-n-shoot method which involves dipping a gelatin layer into a dichromate solution. Personally, I favor mixing the dichromate solution directly into the gelatin, but I realize the dip-n-shoot method has its advocates. The paper deals with the draining procedure following the dipping.

By the way, they have an interesting method of spreading gelatin on glass -- a fine camel hair brush.

[Joe Farina]

I wonder why they include ammonium nitrate in their emulsion?

Have a look at page 86 of the Rallison paper recently posted.

[Steven]

I wonder why they include ammonium nitrate in their emulsion?

Have a look at page 86 of the Rallison paper recently posted.

Many thanks Joe, an interesting paper.

I eventually got the answer from one of your old postings:
http://holoforum.org/oldforum/viewtopic.php?f=2&t=5288

"The addition of ammonium nitrate can make the dichromate several times more sensitive, but decreases the useful life and blue shifts the image. Approximate ammonium nitrate concentrations are usually in a ratio of 1 to 5 by weight to ammonium dichromate up to a maximum of 1 to 1. When the additional substance is washed out of the gelatin a net shrinkage occurs which amounts to a blue shift in reflection holograms..."

Steven.

[Steven]

Hi Steven,

This may have nothing to do with the unevenness problem you mentioned, but just in case, I'm attaching a paper. As I recall, you're using a dip-n-shoot method which involves dipping a gelatin layer into a dichromate solution. Personally, I favor mixing the dichromate solution directly into the gelatin, but I realize the dip-n-shoot method has its advocates. The paper deals with the draining procedure following the dipping.

By the way, they have an interesting method of spreading gelatin on glass -- a fine camel hair brush.

Thanks for the paper Joe.
I think that mixing the AmDi with the gelatin solution would provide the best homogeneous DCG emulsion.
You are correct Joe, I'm doing dip and shoot using mould coated plates. There are several advantages for me using this method.

I'm relatively new to DCG, only being doing it since October 2013, so I still need to hone my mould coating skills and I find that this is best done under full lighting.
I'm using two sets of moulds, 4inch x 15inch, 5inch X 15inch and tend to apply the gelatin generously, which results in a lot of waste.
The waste gelatin can be disposed of easily, it doesn't require chemical treatment and there is a significant saving in AmDi usage.
I don't have any proper darkroom facilities, I have to close the curtains and wait for the sun to go down before I sensitize/expose plates.
I can prepare the gelatin coated plates under full lighting before sensitizing, removing surplus gelatin from edges of plate as well as providing a clear boarder on three sides.
I can have a stock of gelatin coated plates, and just sensitize the number required for a session. I sensitize plates when the sun goes down and expose before the sun comes up.

My main sensitizing solution contains a generous quantity of Ilford Ilfotol wetting agent. I find that using a proper wetting agent is better than using soap. Unless one is very careful, using the latter tends to result in more soap bubbles. I usually dip for 60 seconds and withdraw the plate slowly, the only beading of dip solution I have seen, has been on the gelatin free areas of the glass. The AmDi solution is wiped off the uncoated areas of the plate with a tissue. I usually let the plates dry vertically, but I have tried drying them face down, supported at the two ends 40mm above my work surface. I find that the plates dry quicker when left to dry vertical. There may be a variation in concentration of AmDi between the top and bottom ends of the plate, but I don't have the facilities to measure it. I have not seen blotches in my holograms due to uneven application of sensitizer. It would probably be best for me to dry the plates face down for the first hour, then set them vertically to aid drying. Oh, and I don't have a dust free work area.

Another variable to throw into the mix of course, is that my reference beam does not have an equal power density across it (who's does) despite only using the central third of it's diameter.

I have heard of the camel hair brush method of spreading the emulsion on the glass before.
I think that it may have been from a Chinese paper or video, where they were creating relatively thick coatings using a boarder around the glass substrate to contain the emulsion and stopping it running over the edge.

Steven.

[Joe Farina]

I didn't know there were so many advantages to dip-n-shoot

Obviously you're getting good results, so there's no reason to change your coating method. The hologram with the coins looks excellent.

[dannybee]

ammonium nitrate if I remember correctly it will hyper sensitize the layer, you can if i recall use the vapors from ammonia too

[Steven]

I didn't know there were so many advantages to dip-n-shoot

Obviously you're getting good results, so there's no reason to change your coating method. The hologram with the coins looks excellent.

Many thanks for your comment Joe ref the coin hologram.
It did produce a high grin factor while it was under the magic hairdryer, that's why we do holography isn't it?

There are disadvantages doing dip and shoot:
The emulsion has to dry twice, so it doubles the chance of picking up dust particles.
I don't know if AmDi is absorbed into the gelatin at the same rate as the water in the dipping solution, so I'm unable to determine the AmDi concentration through it's lifetime.
I'm not a chemist and I don't know of a chemical method to determine this.
I do have some cheap plastic cuvettes, so I may design a method using a LED and light sensor to compare the light absorption of my working solution with a known concentration of AmDi, but I have not got around to doing that yet. I suspect that some of the gelatin is dissolved in the dipping solution which would darken on exposure to light, so measuring light absorption to determine AmDi concentration may not be accurate.

Steven