A long post about bubbles

[Joe Farina]

In the past, I've noticed "pits" in my coated emulsion. I call them pits, because they seemed to be what Richard Rallison described in his 1994 Lake Forest notes:

"These "pits" have the appearance of small circles of various sizes and scatter themselves throughout the plate. When the film is processed, the final image has small voids where the "pits" were. So far, the length of the heating time and the peak temperature that cause this have not been determined. In the past, temperature and heating time causing this has fluctuated."

and:

"The causes of film "pitting" are still unknown to us as well as what the "pits" really are. But their characteristics (and that of gelatin) can give us some ideas. It is important to take all known preventative measures for keeping them off the emulsion. Triple filtering helps and avoiding hot spots while mixing helps."

I've never seen a correlation between higher temperatures/length of heating time and the appearance of the pits. But I have seen a clear correlation between bubbles and pits. I was having special trouble with Gelita (280 bloom) photo gelatin. But since I took as many precautions as possible for reducing bubbles, the pits have been greatly reduced, and when they do appear, they are very small in size. One thing which has helped is an ultrasonic bath to partially de-gas the emulsion. My bath is heated but does not include a de-gassing function, so I manually move the bottle of emulsion up and down (in the bath and out) to help break up (?) bubbles. I'm also more careful when the emulsion is pipetted on the plate. I still see a few occasional bubbles, but the problem is greatly reduced.

Are there any other methods to help reduce bubbles?

[Din]

It's not possible to say why these "pits" or bubbles are occurring without further information. It could be making the gloop in a dusty environment without adequate cover, or dust in the mixing vessel. It could be micro-cross linking in the heating gloop, or it could be dust on the plate being coated. If the gloop is heated too high for the gelatin, adding dichromate will cause cross-linking in the mixing vessel, because the heat provides the energy necessary for cros linking. This is the usual reason for 'greenies' or 'blue-is" in a DCG hologram - the cross linked DCG/gel in the mix is already harder than the surrounding DCG/gel mix, so, when applied to a plate there are areas on the plate that are harder in some spots. When this (exposed) hologram is placed in a water bath, the harder areas resist expansion and so the final image has areas of green or blue.This "premature cross-linking" in the beaker occurs at different temperatures for different gelatins, so it's not possible to state the exact temperature causing "premature cross-linking". Another possibility is that the warm air above a warm plate holds more water than cool air; as the plate cools, the warm air above the plate also cools, and so precipitates water onto the cooling plate and the water penetrates into the coating forming micro-bubbles (this is essentially why dew forms in the mornings). This effect may be a consequence of a high humidity in the air - San Diego has low humidity so we never saw this.

Initially, I followed a method used by Don Broadbent (who'd been doing DCG holography since the 70's). This was to heat the gelatin at 60 deg C on a hot plate with constant stirring, then add powdered dichromate, then keep stirring. Then, we'd filter using coffee filters over a beaker, which was on a hot plate. Joy set up a coating station consisting of four glass plates: an upper one, two middle ones (which was going to be the actual DCG plate to record on, so we could coat two plates at the same time) and a lower one. When all the gloop had filtered through, I'd spoon a dollop of the gloop on the upper plate; Joy would draw the dollop across the top plate, onto the middle plate using a (warmed) threaded rod; the excess gloop ended up on the lower plate which was thrown into a bucket with warm water.

But, using these methods, we also noticed these pits and bubbles, and also got a lot of greenies. I realised that some cross linking was already occurring in the beaker due to the gloop being over heated, causing greenies, so we lowered the gloop temp. To avoid undissolved powdered dichromate causing pits, I first dissolved some dichromate in cold water, swilling it around so it all dissolved, and poured the dichromate-in-water solution to the gelatin - not powdered gelatin. To make sure dust from the air was not entering the gloop causing pits, I changed from coffee filters to professional 5 micron filter papers. Also, to make sure the mix was thorough, I added two-three drops of photo-flo to the gloop.

So, our coating procedure was:
1. heat gelatin to not more than 50 deg C on a hot plate with a mag stirrer (not too fast or it'll create bubbles)
2. make a dichromate-water solution (38 mls of water to 8 gms of dichromate if memory serves)
3. At about 45 - 50 deg C, add the dichromate solution to the gelatin (make sure the room light was of!). This was now the gloop.
4. Joy altered a standard coffee filter basket so it'd just fit over a 250 ml beaker. I placed this coffee basket over the beaker with a 5 micron pro filter paper.
5. Carefully pour the gloop into the coffee filter with the 5 micron paper
6. add about 2 to 3 drops of photo flo
7. place thermometer in the beaker and occasionally check the (filtered) gloop, if temp went above 50 deg C, lower temp, and vice versa if it went too cold.
8 Joy set up the coating station, as described above, and i started spooning the gloop on the upper plate
9. We had a very thick glass plate under a standard cooker hood, levelled with some method of ensuring it was level.
10, we placed pennies, four to each corner of a plate (highly standardised NIST traceable!) and, finally, we put the coated plates onto the pennies.
11. We turned on the cooker hood to give a constant flow of air over the plates to ensure no dust settled on the plates while drying.

[Joe Farina]

Thanks for the detailed info.

Also, to make sure the mix was thorough, I added two-three drops of photo-flo to the gloop.

So far, I haven't added photo-flo, but want to try it. When mixing my DCG (I use mag stirrer also) it's obvious that it takes some effort to mix it well. In the glass bottle of emulsion, I see differing levels of emulsion density (striations) unless it's thoroughly mixed with the stir bar. After the emulsion sets for a while, the striations re-appear, and re-mixing is needed. It's the stirring with the stir bar that creates bubbles, even at low speed. The ultrasonic bath has helped a lot. It causes these tiny bubbles to coalesce, and the big bubbles rise to the surface. I asked the AI the question "How does an ultrasonic bath with a degassing function help to remove bubbles from a viscous solution?" and got the following response:
https://www.google.com/search?q=How+doe ... Kw&csuir=1

In case anyone else is having problems with bubbles, they have inexpensive ultrasonic baths with degassing functions on Amazon:
https://www.amazon.com/dp/B0DZ1X4KC2?re ... title&th=1

[Manul]

In the past, I've noticed "pits" in my coated emulsion. I call them pits, because they seemed to be what Richard Rallison described in his 1994 Lake Forest notes:

"These "pits" have the appearance of small circles of various sizes and scatter themselves throughout the plate. When the film is processed, the final image has small voids where the "pits" were. So far, the length of the heating time and the peak temperature that cause this have not been determined. In the past, temperature and heating time causing this has fluctuated."

and:

"The causes of film "pitting" are still unknown to us as well as what the "pits" really are. But their characteristics (and that of gelatin) can give us some ideas. It is important to take all known preventative measures for keeping them off the emulsion. Triple filtering helps and avoiding hot spots while mixing helps."

I've never seen a correlation between higher temperatures/length of heating time and the appearance of the pits. But I have seen a clear correlation between bubbles and pits. I was having special trouble with Gelita (280 bloom) photo gelatin. But since I took as many precautions as possible for reducing bubbles, the pits have been greatly reduced, and when they do appear, they are very small in size. One thing which has helped is an ultrasonic bath to partially de-gas the emulsion. My bath is heated but does not include a de-gassing function, so I manually move the bottle of emulsion up and down (in the bath and out) to help break up (?) bubbles. I'm also more careful when the emulsion is pipetted on the plate. I still see a few occasional bubbles, but the problem is greatly reduced.

Are there any other methods to help reduce bubbles?

Can you take photos? If you want to degass water for an emulsion, I recommend getting an inexpensive distiller, for example, a medical one. The resulting distillate has a low gas content in the first hours after receipt or if hermetically sealed. You can keep a gelatin solution under ultrasound for 30-60 minutes, this also perfectly degasses the solution.

When watering gelatin, there are various defects, some related to wettability, heterogeneity of application, and some stem from the properties of gelatin. A lot depends on the surfactant, as well as the temperature of the substrate and the temperature of the solution.

I must also say that photoflow is not the best wetting agent, it is simply available. Different wetting agents have different effects on gelatin, including defects. I use ilfotol normal result. In my opinion its better fotoflow.

I write through a translator, some points may get lost in translation.

[Joe Farina]

Can you take photos? If you want to degass water for an emulsion, I recommend getting an inexpensive distiller, for example, a medical one. The resulting distillate has a low gas content in the first hours after receipt or if hermetically sealed. You can keep a gelatin solution under ultrasound for 30-60 minutes, this also perfectly degasses the solution.

When watering gelatin, there are various defects, some related to wettability, heterogeneity of application, and some stem from the properties of gelatin. A lot depends on the surfactant, as well as the temperature of the substrate and the temperature of the solution.

I must also say that photoflow is not the best wetting agent, it is simply available. Different wetting agents have different effects on gelatin, including defects. I use ilfotol normal result. In my opinion its better fotoflow.

I write through a translator, some points may get lost in translation.

Thanks for your post. I don't have photos of the "pits" I've seen in the past, although the description given by Rallison above would be accurate. They are circles in the range of 1 to 5mm. I don't know what caused them, but since I took greater care to remove bubbles, they mostly disappeared. I don't understand what a "distiller" is, maybe something was lost in translation.

Regarding the few small bubbles which now appear, I don't know when they were introduced. When making a coating, I gather up a couple milliliters in a disposable plastic pipette, and draw a line of emulsion across the top of the plate. Then draw a Mayer bar across to spread it out (all under a clean hood). It's possible that when the pipette first touches the glass, a bubble or two is introduced at that point, or maybe when the Mayer bar touches the emulsion, bubbles are introduced then. I wonder if a surfactant added to the gelatin would help to reduce surface tension. The temp of the gelatin is 50C and the temp of the Mayer bar and glass are about 40C.

Yesterday I saw an interesting device on youtube and Amazon:

https://www.amazon.com/Resiners-Remover ... hdGY&psc=1

It claims to draw a vacuum of 99kPa or 29.2 inches of mercury, which is very good. The size seems well suited for small amounts of DCG or epoxy.

[Manul]

Can you take photos? If you want to degass water for an emulsion, I recommend getting an inexpensive distiller, for example, a medical one. The resulting distillate has a low gas content in the first hours after receipt or if hermetically sealed. You can keep a gelatin solution under ultrasound for 30-60 minutes, this also perfectly degasses the solution.

When watering gelatin, there are various defects, some related to wettability, heterogeneity of application, and some stem from the properties of gelatin. A lot depends on the surfactant, as well as the temperature of the substrate and the temperature of the solution.

I must also say that photoflow is not the best wetting agent, it is simply available. Different wetting agents have different effects on gelatin, including defects. I use ilfotol normal result. In my opinion its better fotoflow.

I write through a translator, some points may get lost in translation.

Thanks for your post. I don't have photos of the "pits" I've seen in the past, although the description given by Rallison above would be accurate. They are circles in the range of 1 to 5mm. I don't know what caused them, but since I took greater care to remove bubbles, they mostly disappeared. I don't understand what a "distiller" is, maybe something was lost in translation.

Regarding the few small bubbles which now appear, I don't know when they were introduced. When making a coating, I gather up a couple milliliters in a disposable plastic pipette, and draw a line of emulsion across the top of the plate. Then draw a Mayer bar across to spread it out (all under a clean hood). It's possible that when the pipette first touches the glass, a bubble or two is introduced at that point, or maybe when the Mayer bar touches the emulsion, bubbles are introduced then. I wonder if a surfactant added to the gelatin would help to reduce surface tension. The temp of the gelatin is 50C and the temp of the Mayer bar and glass are about 40C.

Yesterday I saw an interesting device on youtube and Amazon:

https://www.amazon.com/Resiners-Remover ... hdGY&psc=1

It claims to draw a vacuum of 99kPa or 29.2 inches of mercury, which is very good. The size seems well suited for small amounts of DCG or epoxy.

https://en.wikipedia.org/wiki/Distillation



The distiller is not expensive and costs from $30 to $50.

If vacuum processing is not carried out correctly, the gelatin will freeze under the vacuum. The emulsion temperature and the plates must be the same. Ideally, the Mayer Bar.

[Tony DCG]

Are there any other methods to help reduce bubbles?

Hey Joe,

A method I used and seemed to work well was when using a syringe to apply emulsion I used a piece of lens tissue as a bubble filter at the output of the syringe. The tissue didn't introduce any dust or debris and filtered out bubbles pretty well.

Perhaps it's worth a try.

Good luck,
Tony

[Joe Farina]

Hi Tony, thanks for the tip, I will keep it in mind. I was using plastic syringes which had silicone oil (presumably) to lubricate the rubber portion of the plunger. Pits resulted after using this (with a syringe filter), but no pits were seen when the emulsion wasn't filtered with the syringe. The "pits" may be tiny droplets of silicone oil, with the gelatin/water being repellant to the oil droplets. I plan to try a glass syringe (w/no lubricant) in the future.

The vacuum de-gasser I linked to works very well. I place a small jar of emulsion in another container with water at 50C (to avoid having the gelatin freeze up) and then apply the vacuum. It's surprising how much it bubbles up. This same device can be used to de-gas epoxy (or anything else) that is used to seal DCG.

[Tony DCG]

Good to hear Joe,

An Ultrasonic cleaner to remove micro bubbles also works well especially if you draw to emulsion from the bottom of the beaker. 20 seconds normally does it.

[holomaker]

I use a disposable pipette , and a taller amber bottle with emulsion sitting in a hot water bath , insert pipette and only suck fluid from the very bottom of bottle , then touch glass plate w pipette tip and then meter out … no bubbles if done smoothly..