Mold coating problem - bad surfactant?

[MilanKarakas]

Hello.

Third attempt to make mold coating failed badly - no single plate is good. My very first attempt (fourth one) was partially successful, but that was just gelatin, without dichromate. Since I am using dichromate I have troubles all the time.

But, I changed something else: surfactant. Since I can't find "Rain-x" in my country, I tried various things, and turns out that silicone oil working somewhat okay. Only one surfactant (water repellent) which I found is "Nigrin's NanoTech" made for clothing purpose (making it water repelling).

After washing out gelatin and dichromate in it, this water repellent still working - not permitting me clean mold glass plate (also this stuff 'migrate' to film side of the another plate, polluting it and made all glass plates unusable for another coating).

What is wrong? Does anyone had similar problem?

Does anyone know which temperature I should use when making molds?

My fridge currently not working properly due to high amount of ice, and Dave Battin's Youtube video said 30 minutes, but did not yield good result. 30 minutes are relative term - depending how fast it can cool down whole box of the plates. It will be good to know which temperature is the best for allowing gelatin to become hard enough to stay in one piece (not 'flowing').

Earlier time I was able to detect problem; if gelatin is frozen, it change look when still between two plates. If not cooled properly, it leave some frosted look on the plate. But now, no matter what I do - it sticks to both surfaces.

My question is: Does anyone use anything else than fancy "Rain-x"? Wax, oil, bat wings?

BTW, recipe for this coating(s) (tried two recipes, one plain KDi, one with Rh6G in it): 100:5:0.5, and 100:5:0.5 + Rh6G, both recipes from: "Improving the holographic sensitivity of dichromated gelatin in the blue-green part of the spectrum by snsitization with xantane dyes", by Dejan Pantelich and Branka Murich.

Gelatin is Podravka's Dolcela (the same thing happening with Dr. Oetker's gelatin, both powder form and sheets). Mixed gelatin two hours, slowly increasing temperature to 48C. Glass plates pre-heated (warm) to avoid dew looking surfaces while applying gelatin, and to make thin layer.


Here is short video to show how it looks:

http://www.youtube.com/watch?v=hULbULvqubs

Thank you in advance.
m--

[holomaker]

hi Milan, ok i looks like your gelatin is cooled enough to create your film, the Rain-x leaves a residue on the mold surface so befor i coat it polish the mold surface (like when you buff/shine you shoes), i suspect good old polishing wax may work as well. Its important to warm you plates prior to coating as well as to leave a space on your shims to allow air to enter (shim along two sides only), again in my offer to you i will include some Rain-x, if you take me up on it...............

[MilanKarakas]

hi Milan, ok i looks like your gelatin is cooled enough to create your film, the Rain-x leaves a residue on the mold surface so befor i coat it polish the mold surface (like when you buff/shine you shoes), i suspect good old polishing wax may work as well. Its important to warm you plates prior to coating as well as to leave a space on your shims to allow air to enter (shim along two sides only), again in my offer to you i will include some Rain-x, if you take me up on it...............

Oh, good grief. You give me excellent idea. Paraffin wax (or beeswax, just need to see whether it is water soluble). If anything is impossible to glue, then wax is the best choice. Also, will try liquid wax (I doubt it is wax actually, maybe some oil) for garden torches. Yet, unknown parameter is what will happen when cooled down to about 5C. Maybe it will shrink and crack due to low flexibility at low temperature. Or, something else which is hard to glue...

Applying to the glass surface may be done by veil method or Meyer's bar. Maybe there is an issue due to relative low melting point, and heating glass plates with hair dryer prior to applying gelatin may be tricky (not for liquid paraffin). Will try it right now.

I will PM you about your offer, already waiting answer from previous one.

[holomaker]

Milan did you also see the youtube on Vail coating i did ? The wax should work, just be sure to polish it befor coating !

[MilanKarakas]

Milan did you also see the youtube on Vail coating i did ? The wax should work, just be sure to polish it befor coating !

Thank you Dave. Seems that I made few mistakes with surfactant I have (still, I think Rain-x is much better).

First, I did not read user manual on the spray bottle carefully saying "shake before use".

Second thing: I did not clean glass properly as I am doing with plates where film will be at end. This is because 'the old way' with silicone oil (or mineral oil, not sure what I had) stick very well and working modestly.

Third thing: I did not wait long enough allowing spray solvent to evaporate (that is big difference between Rain-x and this one: spray!). At first, surfactant is not very viscous, but after a while, it become like butter. Then is time to polish, not before. Something is added in spray bottle which not working if I put gelatin too soon (even after half hour). It should be sprayed firmly, then polished, else... not working. Will try to do mold coating again (last time with this stuff if disappoint me again).

Now testing new approach - first cleaning glass, then shaking bottle thoroughly and applying spray. Waiting, while heating little bit to push out solvent. When it become less stinky, then tried water - it working. Tried quickly cool down to 5C in the fridge, and water drop still move freely (although, not happy as it is at room temperature).

I hope it will works.

Best--
m--

P.S. Dave, it is paid right now (there is date... two days ago, but they didn't send me notification).

Thank you very much!

[Joe Farina]

Hello Milan,

I am gaining a little experience with the mold-coating method, and would like to mention a few things:

While I've only used Rain-X so far, Cristiano Perrucci (in Italy) uses a product called "Rain Clear." I would guess that a variety of mold-release materials could be used, but you would have to do your own trials.

It's important to make sure your other glass plate is very clean. Years ago, Dave Battin suggested the use of TSP (trisodium phosphate) and I tried it. Ever since then, that's all I've ever used, and never had a detaching problem with DCG or MBDCG. I mix the concentrated TSP in hot water, soak the glass for about 5 minutes, scrub the surface with a sponge, let it soak for another hour or two, scub a second time, rinse in tap water, rinse in distilled water, then dry with paper towels.

Be sure to use only two strips of tape as Dave mentioned.

So far, I've only used the mold method with MBDCG, but I've found that it needs to set for a pretty long time (at least with the formula I'm using) before opening the mold. My MBDCG (with boric acid) has very weak adhesion to the glass immediately after coating, but it gradually (over many hours) becomes quite strong. So I would try waiting say 48 hours before opening the mold, and see if that helps. I had detachment problems with short periods.

[dannybee]

here a nother thought too, ive tried this and it works, put the tape on the mold release side and rain-x or what ever on the tape too, this way you just have to pull them apart and let dry

[MilanKarakas]

Hello Milan,

Hello Joe.

I am gaining a little experience with the mold-coating method, and would like to mention a few things:

While I've only used Rain-X so far, Cristiano Perrucci (in Italy) uses a product called "Rain Clear." I would guess that a variety of mold-release materials could be used, but you would have to do your own trials.

Past few days checked in town whether someone has 'rain-something', but nobody has it. Only "Nigrin's" product which is intended for clothing, not for glass. Noticed that if water is freshly applied, then it goes away, but if standing on the glass ten or more minutes, it doesn't want to leave surface so smoothly - definitively something is wrong with this one. Tried various things, and silicone oil works better than Nigrin, But test in freezer at 5C showed not so good properties - water remains on the plate when tilting.

It's important to make sure your other glass plate is very clean. Years ago, Dave Battin suggested the use of TSP (trisodium phosphate) and I tried it. Ever since then, that's all I've ever used, and never had a detaching problem with DCG or MBDCG. I mix the concentrated TSP in hot water, soak the glass for about 5 minutes, scrub the surface with a sponge, let it soak for another hour or two, scub a second time, rinse in tap water, rinse in distilled water, then dry with paper towels.

Yes, I understand. Tried clean few plates again, but the result is the same. It works somewhat, but not good (at least with water). Maybe I should stick to veil coating for a while until solve this problem. Enjoyed in 'clean room' for three days, but today disassembled fan and filters (improvisation) because of need for space in the room (installing stove for the winter time). 60 W fan, three speeds, rolled about 2 m long tube with polyethylene fabric intended for protecting plants against frost, and run at maximum speed. After one hour, dust are reduced to fine particles. Then reduce speed to lowest one, and leave all three days. Only when entering room - dust begins to flow in. Laser beam is almost not visible. Very spooky feeling. Will rebuild even bigger filter.

Be sure to use only two strips of tape as Dave mentioned.

Okay, this time I used four strips of the tape, but leaved four channels where excess of the gelatin will leave the sandwich. Will remove that two tapes. I did it because wanted nice border at all four edges.

So far, I've only used the mold method with MBDCG, but I've found that it needs to set for a pretty long time (at least with the formula I'm using) before opening the mold. My MBDCG (with boric acid) has very weak adhesion to the glass immediately after coating, but it gradually (over many hours) becomes quite strong. So I would try waiting say 48 hours before opening the mold, and see if that helps. I had detachment problems with short periods.

48 hours?! Oh, well. Hmm... This is maybe reason why gelatin is not set properly. On video it looks like it is, but it is still kinda soft. I used exact recipe as is described in Pantelic's article - 100:5:0.5, and aside unsuccessful mold coating I made two small plates with veil method. There is almost no dichromate at all. Plate is pretty transparent, not a trace of yellow color. Probably film is too thin and amount of dichromate is too low (only 10% of dry gelatin). And, amount of gelatin is too low, 5% of water content.

I did not paid attention to the whole document, there is significant difference: they use microscope slide and put gelatin onto it (don't know exact name, I think "gravity settling" or so). So, by 'gravity' my thought was that this is different name for veil coating. I am badly wrong about that.

And next time I should wait longer time to set and firmly checking gelatin, not sloppy as I did. Plus, will add more gelatin and other chemical proportionally.

BTW, tried testing both recipes, one with Rhodamine 6G and one without. Having problem at the start. Calculated how much minutes I should expose plates, but no matter what - very poor result. Then noticed logical flaw in my thinking about 'narrowband' vs. 'broadband' processing. Film is very thin, and all the time I am thinking how to make it narrowband so that it is brighter. My logic was followed by idea and comparison with lasers: if laser has many spectral lines, each of it is weaker, so less lines - the stronger laser. But didn't recognize that this comparison is bad; it should be compared with dichroic mirrors - the more mirrors, the brighter the hologram.

Then tried re-process few holograms and got amazing increasing in brightness and more reddish appearance. And, got something which was hidden in UV range. For now, my last test and comparison of that two formulas failed because too low content of the dichromate (and emulsion as well).

Thank you all for help.
m--

[MilanKarakas]

Something bothering me about time spent doing mold, and time required in the fridge to set gelatin. What if I spent too much time stacking molds in the box, then whole box put in the fridge. What if gelatin don't like too rapid cooling? My fridge is empty now and cooling very rapidly.

If gelatin has 'strands' (I don't know exactly what is happening here), and such strands need to be 'interwoven' somehow in order to set, and become gummy. Last formula has very low amount of gelatin, just 5%, so maybe water re-dissolving it even at low temperature? Or, maybe 5C is too low temperature for gelatin? Or maybe opposite happening - viscosity at 5C is too high and thus slowing down everything?

Very brief explanation on wikipedia about what is the "Bloom test":

"Bloom is a test to measure the strength of a gel or gelatin. The test was originally developed and patented in 1925 by O. T. Bloom. The test determines the weight (in grams) needed by a probe (normally with a diameter of 0.5 inch) to deflect the surface of the gel 4 mm without breaking it. The result is expressed in Bloom (grades). It is usually between 30 and 300 Bloom. This method is most often used on soft gels. To perform the Bloom test on gelatin, a 6.67% gelatin solution is kept for 17-18 hours at 10°C prior to being tested."

(important parameters in bold and underlined)

So, 17-18 hours at 10C for gelatin of 6.67% (100:6.67:X). If Bloom test is for pressing, or mechanical stress, then pulling mold apart cause stress as well, where gelatin at such short time did not set properly: only 2 hours, planed even shorter - 30 minutes, but my fridge was full of ice at this time, so I decided to wait more.

Maybe it is good to change setting on the fridge from 5C to 10C at one part of it (I have thermometer probe which can protrude box with plates, so can control whether it reaches such and such temperature)?

Also, I am not sure at all in my gelatin I use (Podravka's Dolcela). On the net, there is some information about food grade gelatin, but that figure may be somewhat inconclusive:

"Gelatin used in food usually runs from 125 Bloom to 250 Bloom. There are several different grades of sheet gelatin. The most popular are Silver grade (160 Bloom) and Gold grade (190-220 Bloom). Typically the higher the Bloom, the more you can expect to pay."

I have Dr.Oetker "Gold extra", and I hope this means "Gold grade" (190-220 Bloom). The reason what I did not use it in past time is observation that both; powdered form and leafs give me somewhat less clear mixture, but that may be completely subjective. And, that statement about the price; both gelatins are almost the same price - not related to the quality of the gelatin, but rather on market prices (First one is 'domestic' product, another one is imported).

---

Aside all that problems, another problems are with understanding Pantelic's document:

"The dependence of diffraction efficiency on the concentration of Rhodamine 6G is shown in Fig.3. As the concentration of Rhodamine 6G increases, the diffraction efficiency increases; it reaches a maximum when the dye concentration is 7.5 mg/l. After the maximum concentration is attained, the diffraction efficiency decreases because Rhodamine 6g precipitates at higher concentrations in the presence of the dichromate ion."

Fig. 3, from Pantelic's document.

It looks too 'sharp' to me, but that is because scale is from 20-32% diffraction efficiency, not gain in the sensitivity. Another graph showing absorption curve, where it looks like DCG + Rh6G has little bit over 100% more absorption, and if this means doubling gain, then it is worth messing with. But in text, there is value of sensitivity increasing from 215 mJ/cm^2 to 140 mJ/cm^2, which is more in agreement with graph above, or increasing of the sensitivity of 60% (still not bad).

The absorption graph:

Some comparisons of DCG and dyed DCG...

Also, there is problem how to calculate concentration of the Rh6G if I want to increase gelatin content (for example from 100:5:0.5 to 100:10:1)? I made stock solution of 75 mg/l (the most difficult part is to weight such small amount, and I had limit of hundreds of milligrams - impossible to measure tens of milligrams). This solution then is diluted 1/10 to the mixing solution, i.e. 90 ml of water, 10 ml of concentrated solution.

I will try to make mold coating again, and this time will try to increase concentration. But, this time will leave it longer in the fridge (maybe 12 or better 24 hours) and frequently checking whether it set or not.

Best--
m--

[Joe Farina]

Hello Milan,

After thinking about the difficulties you mentioned, maybe using the veil coating method would be good, at least for now. Without a laminar flow area, veil coating and Mayer bar will produce similar results -- dust will settle on the surface of the emulsion. But since you're in the early stages of experimenting, that problem can be solved later.

As for mold-coating, please have a look at the Wiki (if you haven't done so already) in the MBDCG section. It was mentioned that an ammonia-based window cleaner (i.e. Windex or Glassex) works well for cleaning glass prior to mold-coating. That should be easy to get. Also, Ahmet mentioned that ordinary car-wax works well as a mold-release.

Since your supply of Rhodamine 6G is very limited, I would put that idea on the back burner for a while. There is not enough information out there to tell you exactly how much R6G to put into DCG to make it more green-sensitive. A lot of trial-and-error work is needed, and I don't think you have enough material for this. Wait until you get a few more grams of R6G.

Since the results with G307 were encouraging, maybe you could go back to that. It would be really nice to see you get some good images with that system. Alternately just try classic DCG (with high dichromate concentration, which is necessary) at 532nm. If your laser is doing a stable ~40mW, then you should be able to make good holograms that are small in size, say 5 X 5cm.