"Blooming" of gelatin?
Can someone offer an explanation of why all the alternative processes state hard gelatin (photo grade) has to "bloom" before it can be used? What's going on during this cold water phase? That is, why is it necessary for gelatin to sit in cold water for so long before it's finally heated up and goes into solution?
I've let gelatin sit and bloom, and then I've also taken the gelatin granules right out of the container and dissolved it in hot water right away. It works both ways (I use it as paper sizing). I'm curious, what's going on during the blooming step and why is it required?
This step is done to allow the gelatine to absorb water and dissolve evenly and not clump. The same thing is done when using gelatine for food purposes.
If it bothers you, omit the step and just wait! ;)
After a few hours waiting, it will teach you that allowing for blooming is not all that bad! ;)
Honestly, I've kinda wondered the same thing. I usually allow for this bloom so I haven't seen the negative impacts of not doing it, but now I'm curious what happens if omitted.
I bloom gelatin either in cold water or in the emulsion make itself, depending on the amount of water needed and the amount of digestion needed. Adding gelatin solids directly to the emulsion before digestion will allow the gelatin to bloom during the digestion and will limit the amount of extra water added. However, this "bloom" takes up to 1 hour, so the digestion should be planned to last that long as well.
The swelling of gelatin in cold water followed by a melt serves two functions:
1. Directly mixing gelatin in hot water introduces air bubbles due to the agitation of the mixture. Heating a swollen gelatin to a liquid state allows the mix to degas.
Commercial film coating is typically accomplished without this swelling stage. Heated mixing kettles capable of holding 750 -1500 liters feed into devices that filter and degas the mix.
2. The bonds of the polypeptide chains formed by a swell/melt gelatin mix are somewhat stronger than a directly mixed and heated one. This is probably more important for alt processes that rely on cross-linking for image formation.
For these situations, mixing conditions are avoided that introduce bubbles, and antifoamants are present to suppress bubble formation.
In modern making and coating, the addition of solid or even bloomed gelatin is avoided. With modern wash methods, gelatin is added at between 12.5% and 22% (the latter as either pellets or as a syrup). The volume is then readjusted during the wash operation to give the desired volume and gelatin content. This is usually 1 kg / mole of silver and between 5 and 10% gelatin.
I have never heard of nor experienced the change in bonding Charles. Perhaps it takes place with some gelatins. I do know it happens if you heat the gelatin too much under extremes of pH, either acid or alkaline or if you heat the gelatin over 70C for an extended period. I avoid all of these.
Original poster here. Gerald, Charles, thanks for your replies. I must reiterate I'm using gelatin as a paper sizing, not as an emulsion.
Air bubbles, digestion, noodling, molecular weight, I'm not doing any of that. I'm not making film. Now in the future I want to use gelatin as a base/emulsion for printing on ceramic or glass--then that will be very useful information.
Again, for sizing paper, numerous books I've read and various websites state to allow the gelatin to bloom but never why. I've let gelatin bloom as described....
....and then I've also simply put a measured amount of dry gelatin granules in a glass lab beaker, filled it with hot water and then placed the beaker in a hot water bath to keep the temperature up. Some slow stirring with a glass rod, the gelatin melts and it looks identical to the cold bloom gelatin. Is this wrong?
Generally, for the purposes you describe, to make 10% gelatin for sizing:
900 grams of water at room temp (20C)
100 graams of 250 BI gelatin (Bloom Index which has nothing to do with blooming gelatin)
Gently stir the gelatin into the cool water and begin warming to 40 deg C. Hold there until all gelatin has melted and dissolved. Add preservative and chill set until use.
This entire process is called Blooming.
There is an alternative method also called blooming and is used for addition of solid gelatin to an emulsion or any gelatin based alternate process.
Take 100 g of gelatin and add small increments of ice cold water (under 10C). Just wet the gelatin and then allow it to worm to 20 C while absorbing that cold water. Record the weight change. This gelatin should not be stored but rather used immediately.
When needed in your formula, add the required amount of Bloomed gelatin noting weight of gelatin and water to get your total change.
In many cases, this sort of blooming step is omitted and gelatin is added directly to the hot light sensitive mixture.
So, as you see, there are basically 3 methods of getting from here to there and two of them are called blooming gelatin but use entirely different methods and which are often used for different purposes.
I hope this sheds more light on the terminology and your question. Sorry about the confusion.
It sounds like the OP wishes to have as little fuss as possible when it comes to sizing. With that in mind, if the method seems to be working, and the hardener is still getting that gelatin to a sufficient level of insolubility, then no harm no foul I guess.