Blending Gelatin sensitizer Solutions-completing Gelatin Plate

It’s not exaggeration to say that the gelatin plate is the life of collotype. How prints appear changes depending on how to blend gelatin sensitizer. There used to be a lot of collotype printing companies, and the same numbers of recipes existed.

Following is the current blending recipe of Benrido Collotype Atelier.

Gelatin1 　　　　　　　 720g
Gelatin2　　　　　　　　 720g
Water　　　　　　　 　　　　 15000ml
Ammonium Dichromate　　 180g
Potassium Dichromate　　　 180g
Lead nitrate　　　　 　　　　　 30g
Benzoin　tincture　　 　　　　 180ml
ethanol　　　 　　 　 180ml


Blending of gelatin sensitizer 1 : chemicals
Above chemicals are broadly separated into three categories.
Ａ） Gelatin
Ｂ）Sensitizing materials: Ammonium Dichromate, Potassium Dichromate
Ｃ）Assistants: Lead nitrate, benzoin tincture, ethanol



Two kinds of gelatin :720g each



Main ingredient of sensitizer is gelatin. Gelatin for collotype once existed but has been discontinued as decline of collotype. And then we used photographic gelatin. But today, it’s not easy to purchase photographic gelatin anymore because of digitalization.
So now, we uses gelatin for food of Nitta Gelatin inc.

We did various tests when we were changing photographic gelatin to edible one. We judged gelatin’s aptitude for collotype by stiffness/softness, viscosity, strength of gel, tones, and printing-resistance. As a result of tests, now we decided to blend the same amount of two kinds of gelatin: 1)high-viscosity, soft gelatin 2)Low-viscosity, tough gelatin.






Ammonium Dichromate (NH4)2Cr2O7

180g

　Potassium Dichromate K2Cr2O7


180g

Potassium Dichromate, itself is resistant to light. However, it responds to light quickly when it combined with organic matter. Two kinds of Potassium Dichromate are necessary for collotype.
Each of them has different characteristics. Ammonium Dichromate is more photosensitive than Potassium Dichromate. On the other hand, Potassium Dichromate has better preservability because it has milder photosensitivity compared to Ammonium Dichromate. When collotype was invented, only Potassium Dichromate was used. Later, recipe of blend same amount of two kinds became popular. Benrido follows it. However, the record in 1981 shows there was a company which mixed two kinds of Dichromate 10:69 but not 50:50.




Lead(Ⅱ)Nitrate Pb(NO3)2

30g

When mixing Nitrate with dichromate, it forms yellow lead chromate. Unclear Yellow color helps to see picture when exposure and ink when prints. It is said that using Nitrate was started in Japan. In Europe, Nitrate is not used. So, plates are clear.






Benzoin Tincture 180ml

Use of Benzoin Tincture was also devised in Japan. When gelatin sensitizer is put and dried, small spots appear on the surface of sensitizer. If spots are left, spots will appear in images.
Benzoin Tincture prevents spots from appearing. We mix it with ethyl alcohol in gelatin solution.





Blending of gelatin sensitizer 2: mixing chemicals





Gelatin (center) two kinds of dichromate (left) Nitrate(right)




Bathe two kinds of gelatin, 720g each in 12L of purified water, and let it swell. Dissolve the gelatin by putting the bowl in hot water for one hour.
Add 1L purified water each to two kinds of dichromate and nitrate. And dissolve them by putting the bowl in hot water as gelatin.
If you bathe gelatin in water too long, gelatin starts to melt, intensity of jelly decreases, and becomes no longer useful.



Add Ammonium Dichromate into gelatin solution.


And then, add Potassium Dichromate K2Cr2O7


Alcohol (upper), Benzoin Tincture (lower)


At last, add Nitrate.


Adding nitrate changes solution into bright yellow.


The first filtering with a funnel and a cloth


This recipe makes gelatin sensitizer solution for a couple of days.



Let it cool off and leave it for one night to make it mature. More than 10 hours is necessary for maturing process. By maturing, plates gain strong printing resistance.



Shitahiki treatment

Let the gelatin sensitizer sleep for one night, and at the next day, making of gelatin plate is done. Shitabiki is done as a pretreatment of gelatin plate making. It works as middle layer to connect glass surface and gelatin sensitizer surface. Without this pretreatment surface of gelatin layer falls off.
Main material is water glass. As an additive, we use beer. Some uses gelatin or the white of eggs but beer is the most stable.
Brand of beer doesn’t matter. But no low malt beer (we tested).



Sodium Silicate Na2Si4O9











Solution of beer and water glass. 3ml of Water Glass+ water 30ml and beer 30ml



Applying Shitabiki solution

Place shitabiki finished glass plates in dryer machine horizontally.


There is another way of shitabiki, but Benrido does a cloth wiping style “Shitabiki”. After Shitabiki treatment, put plates inside a dryer adjusting to make it horizontal.














completing Gelatin Plate


Leave gelatin for one night. Melt it again.



Saponin 13g＋Water180ml（For three days）


Dissolve gelatin in hot water, again.
Filter it (Second time). Adding Saponin to it just before putting it on the glass plate. Saponin activates surfaces. It prevents gelatin from lathering.



Put Gelatin sensitizer solution on pre-treatment (Shitabiki) finished glass plate.



Make it even.



Delete bubble by picking if there is any.


Require two people to treat the biggest sized glass plate.



Place the glass plates in dryer machine horizontally.




Dry for 1hour and half at 55℃.



When it becomes normal temperature, drying process is done.
Put them in dark for exposure process on the next day.