Some newbie questions about DCG

[Joe Farina]

I would try to "tinker" around the temperature of your water (= "swelling") bath. Most of the time I was doing a couple of methods of gelatin sensitization (dichromated, ferric, several types of monomer, occasionally even AgX), I used to do it with culinary gelatin. Controlling the temperature of the swelling bath seems to be of utmost importance for soft gelatin like this. Depending on the kind of sensitization, exposure levels etc. the optimum may be anything from 15 - 35°C. The range of tolerance from getting no hologram at all to a noisy, milky one may be very narrow: So setting the temperature of your swelling bath at say, 15°C may be a good start...

That's a good point.

[Mihai]

That's an interesting way of testing hardness. Could you please elaborate on it? I assume that, since hard gelatin swells less compared to soft gelatin, less water is absorbed. Thus for an equal number of grams of gelatin, the "swelled mass" which weighs the least is the hardest gelatin. Do you keep the amount of swelling time constant for each sample, and do you have to "skim" the excess water from the top of the container before weighing it?

I can't take credit for this testing method, I found some info about this here: http://www.holowiki.org/index.php?title=Gelatin I used a lot more water than needed for the gelatin to swell, and I let it swell for more then 15 minutes, it won't swell more, no matter how much water is in the container or how long you leave it there, given the temperature is constant. After that, i pass it trough a tea strainer and weight it.

I would try to "tinker" around the temperature of your water (= "swelling") bath. Most of the time I was doing a couple of methods of gelatin sensitization (dichromated, ferric, several types of monomer, occasionally even AgX), I used to do it with culinary gelatin. Controlling the temperature of the swelling bath seems to be of utmost importance for soft gelatin like this. Depending on the kind of sensitization, exposure levels etc. the optimum may be anything from 15 - 35°C. The range of tolerance from getting no hologram at all to a noisy, milky one may be very narrow: So setting the temperature of your swelling bath at say, 15°C may be a good start...

I didn't knew about that, but i will try swelling it at different temperatures. I usually let it swell at room temperature (about 20°C) and then dissolve it on am makeshift double boiler at 58-60°C. And with the plates that didn't show any hologram, i think happened what Joe said, turned to uv, as I remember one of the plates, when it was in the last alcohol bath, the hologram appeared red, then passed through the whole spectrum and finally disappearing, before removing it from the alcohol bath, and after drying, I had a clear plate, but no hologram. At least not a visible one. If this happens again, I will try post-swelling with sorbitol or citric acid.

[Joe Farina]

I found some info about this here: http://www.holowiki.org/index.php?title=Gelatin

Thank you Mihai.

With regards to the "swelling bath," Martin was referring to the water bath after exposure, and just before the alcohol(s). If you're using room temperature baths for the water or alcohol, and still getting milkiness, it might be possible to use cool liquids from the refrigerator. This might prevent milkiness, but it would probably be more convenient to use a harder gelatin and room temperature baths.

[Martin]

With regards to the "swelling bath," Martin was referring to the water bath after exposure, and just before the alcohol(s).

Quite right.

If you're using room temperature baths for the water or alcohol, and still getting milkiness, it might be possible to use cool liquids from the refrigerator.

Another option might be adding alcohol etc. to the water (maybe up to 30% or so) - in order to reduce the swelling of the layer.

[Tony]

I'm surprise the question of gelatin bloom isnt a bit more front in center. I would say this should be addressed before all others. If we are dealing with a 200 bloom gel there may be some cause of concern.
Film aging might be an issue. Perhaps after coating you should concider a long drying phase, perhaps 3-4 days in a cool dry place.
Good luck to you
T

[Joe Farina]

The bloom strength is often mentioned in connection with DCG. Rallison also calls this the "jelly strength" and is measured with a Bloom Gelometer. The gelatins he used (in the notes I have from Lake Forest) had bloom strengths in the range of 215 to 235. I forget what the bloom strength of Knox gelatin is, I know that John made a phone call to the company and found this out.

I know that bloom strength is not the same as "hardness." But to be honest, I just consider bloom strength to be one and the same as "bias hardness."

Hardness, bloom strength; basically the same to me. I wonder if there's a reason to look at it differently.

For exposure around 450nm with 3-30-200, the bloom strength of Knox seems good to me.

[Joe Farina]

I checked the old forum (actually I think John first posted it on Network54) and according to Kraft, the bloom strength of Knox gelatin is around 235. It would be interesting for someone to do swelling tests (like Mihai did) using Knox and some other (i.e., European culinary) gelatin. I think that would be a more accurate way to compare them, than relying on company information. If someone feels like doing some testing, I will send some free Knox.

[Tony]

Granted Joe, but there are also a fair amount of types of gelatin, including pig, cow and the occational Iguana. There are also A and B types.
I think it is a great idea to send Mihai some knox. This would at least base line things. Its seems to me anything outside the basic DCG formula is likely to lead into a road not well traveled. If the basic proceedure does not result in a decent hologram then it stands to reason that the gelatin might be the problem.

All the best and best of luck
T

[Martin]

Granted Joe, but there are also a fair amount of types of gelatin, including pig, cow and the occational Iguana. There are also A and B types.

Yes. I would also have thought there might be other factors than bloom strength that play an important role here. I used to consider bloom strength as something affecting the setting and melting point of a gelatin at a given concentration. By other factors I'm particularly thinking of the chemical composition of a particular gelatin. In one of his latest posts here, Jeff alluded to the importance of the sulfur groups.

[Johnfp]

Anyone who is using something other then KNOX may be able to call the company and get the bloom and type of gelatin from them.