Potential for Multiple layers with emulsion coating

[rdg]

I have never played with coating emulsions, or even started to make my own emulsion for that matter, but know that I am likely going to be doing it later. In doing a great deal of reading I have more questions than answers.

I know that this is substantially above creating and coating my first emulsion but is it possible with hand coating to do multiple layers? And if it is possible would it be preferable to do them sequentially as part of the same coating session or would it be better to wait and do it after the previous layer(s) have hardened/stiffened?
As I see it, and with my experience I more than likely can be very wrong, having the ability to have multiple layers with hand coating will allow for such wonderful things as an anti-halation layer or even a top protection layer for the emulsion. I also realize that this would be imperative if anyone wants to ever coat colour emulsions by hand.

Thanks.

Richard

 

[Photo Engineer]

Richard, I have coated many layers on Baryta paper, RC paper, and film. It is almost impossible to do a good job on Baryta due to curl. Also, on any support, defect rate goes up with the # of layers, but it is not excessive. We usually got on the order of 18 good sheets out of 24 coatings.

Each layer must dry before the next one is applied or you scratch or scrape the wet previous layer. In fact, you have to use the right coating blade for each layer to account for the "height" increase due to the previous layer(s). So, you might coat at 5 mil, then 7 mil then 9 mil and etc to clear the previous layer and yet apply the right amount of emulsion.

PE

 

[rdg]

Thank you. I was thinking about the same thing, although when to add the new coating was not something I was certain about.

I am not yet ready to try it, there is a lot of things I have to learn and do first, but at least I know that the potential exists.

At what point does the emulsion start to become too thick? Considering the number of layers that existed for colour films, although I am not saying that the layers would be the same thickness as with hand coating, there is probably a practical limit, beyond where additional layers are prone to failure just from the coating techniques.

Again thanks.

Richard

 

[Photo Engineer]

Richard, the first layer is thicker than zero and thus has an effect.

PE

 

[dwross]

The thickness with handcoating adds up really fast. The thinner you try to coat, the more difficult it is to get a smooth, uninterrupted coating, especially after the first one. It's far easier to get nice multiple coats on glass plates with a passive pour technique. But, you still have the problem of thickness. It's not a very thick total coating that becomes too thick to fix evenly, or at all. This is especially true if you add hardeners to any of the layers.

Beyond the mechanical problem of hand coating very thin, there is capability of the emulsion chemistry itself to deliver the goods when it is coated very thin. Gawd knows I love the old emulsions, but they are not the most efficient dmax delivery systems. (To be clear, that is the reason they are so beautiful and different from what you can go out and buy.)

If you want multiple coats, you'll be happier with a more 'modern' emulsion -- unless the goal is something totally artsy. Near-modern emulsions can be made in a home darkroom, but it takes a lot of practice and commitment to technique. Standing on my favorite soapbox, I can only recommend that anyone interested start simple.

 

[Photo Engineer]

I have coated multilayer materials using our lab equivalent of AJ-12. We coated 6 layers. It is a matter of practice and attention to gelatin and other chemical "load".

PE

 

[cliveh]

I have coated multilayer materials using our lab equivalent of AJ-12. We coated 6 layers. It is a matter of practice and attention to gelatin and other chemical "load".

PE

PE, you obviously advocate this, so can you say why multiple layers are beneficial?

 

[wildbillbugman]

How about putting a nonreactive clear coat between each layer? To prevent damaging each coating with the next coating. I think that glass plates will be more conducive.to multiple coats than clear plastic. Although I have never succeeded making in-camera negatives with multiple coats, I have been making multiple final coats on glass for more years than I like to admit. Think multiple decades.
Bill

 

[Photo Engineer]

Clive, I can give several reasons!

One is to put on a protective overcoat for your film or paper. You can also add matting agents to change surface characteristics. Examples are starch in gelatin. Great matting agent.

Another is to put on two different speed emulsions to extend the latitude. Or, if paper, to create a VC paper with emulsions of 2 different contrasts but the same speed. I did some work on this with my Azo type emulsion AAMOF and described the potential here on another thread.

And, of course there is the application to color!

PE

 

[RauschenOderKorn]

Or, if paper, to create a VC paper with emulsions of 2 different contrasts but the same speed.

That is the way Ilford describes their VC paper: several layers, sensitive to different wavelengths of light (blue and green). What has me puzzled is the VC Emulsion by Rollei/Maco: They have a VC liquid Emulsion which comes in one container, so you coat only one layer. How is that made? Can you mix 2 emulsions with different sensitization and thereby get a"combined" result similar to coating two layers?

 

[removed account4]

That is the way Ilford describes their VC paper: several layers, sensitive to different wavelengths of light (blue and green). What has me puzzled is the VC Emulsion by Rollei/Maco: They have a VC liquid Emulsion which comes in one container, so you coat only one layer. How is that made? Can you mix 2 emulsions with different sensitization and thereby get a"combined" result similar to coating two layers?

im not PE and i have no clue ..
but i have coated paper with 2 different emulsions .. one home made and one store bought ..
interesting results to say the least !

 

[RauschenOderKorn]

Don´t get me wrong, I am not against coating various layers for whichever purpose. I am sure that especially in the artistic area, you can get spectacular results with multiple layers

I am just curious how Rollei/Maco is able to do VC with one layer, if this is true VC (e.g. as decribed by Ilford) and not just an sensitization effect (I imagine that might be possible.)

 

[Photo Engineer]

Yes, you can mix emulsions in a VC paper, but you have to face up to several problems associated with keeping.

PE

 

[RauschenOderKorn]

Yes, you can mix emulsions in a VC paper, but you have to face up to several problems associated with keeping.

PE

I was wondering about how to keep the sensitiser from "cross-contaminating" in the mixture. I assume that is part of the problems with storage?

With regards to DIY: is it be as easy as preparing two identical emulsion - one ortho and one without sensitiser, ripened to about the same speed - and then mixing just before coating? Or is there a trick?

 

[Photo Engineer]

It is that and one other problem which is the trick. Yes you can mix emulsions with different sensitivities but they also have to be different speeds and for best results have different contrasts. After all, that is what you want, variable contrast. So, you have two rather different emulsions that, for best results, should be kept isolated.

PE

 

[AgX]

I was wondering about how to keep the sensitiser from "cross-contaminating" in the mixture.

Agfa solved this issue.

 

[RauschenOderKorn]

Agfa solved this issue.

As far as I know Agfa developed a system of symultaniously coating various layers, right?

But actually I was not refering to coatings made on an industrial scale, but literally to the Foma VC-Emulsion sold in a plastic container to hobbyists. Foma hardly can predict the storage and transport conditions & temperatures and storage times can be long. In the plant of Agfa / Ilford / Kodak / Adox, / ... all these variables can be controlled. The DIY-Emulsion is beyond the manufacturer´s controll once it leaves the plant.

 

[AgX]

As far as I know Agfa developed a system of symultaniously coating various layers, right?

No, that is industry standard.
What I referrerd to was the Agfa's way to counteract sensitizer dislocation when mixing two differently senstized emulsions, by having one contain a certain stabilizer.

 

[Nodda Duma]

For hand-coating multiple layers glass, I've run into issues with unintentional mixing of the layers due to the fact that, after the first layer, you are pouring melted emulsion onto unmelted emulsion..which then melts the first layer. If the layers have different photographic properties, this can lead to a greater or lesser non-homogenous silver density "swirl" looking effect in the final image depending on your specific coating technique and the specifics of the coating layers (it is analagous to coating wet paint over a different color wet paint..google swirl painting for an idea of what the effect is). I've learned this lesson the hard way.

Use of a coating well like what PE and Denise Ross have used will help minimize this issue, as well as a coating machine setup if you're super ambitious. Another solution is to harden each layer as you go (or have a separating thin hardening layer between emulsions), raising the melting point of the previous layer above the temp of the emulsion to be coated. You have to allow sufficient time for the hardener to set in before applying the next layer, so multiple layers will take many days to do. This latter approach is related to what PE refers to above about keeping the layers separated.

 

[Photo Engineer]

As far as I know Agfa developed a system of symultaniously coating various layers, right?

But actually I was not refering to coatings made on an industrial scale, but literally to the Foma VC-Emulsion sold in a plastic container to hobbyists. Foma hardly can predict the storage and transport conditions & temperatures and storage times can be long. In the plant of Agfa / Ilford / Kodak / Adox, / ... all these variables can be controlled. The DIY-Emulsion is beyond the manufacturer´s controll once it leaves the plant.

Kodak actually invented this, and Agfa was unable to use the method until they changed to Kodak style couplers in color materials.

It is possible to coat multiple layers by coating, drying, coating, drying and etc. The trick is to harden sufficiently between steps. However, that said, it is possible to mix two emulsions with different sensitizations as long as the size frequency distribution of the grains is similar and the halide content and distribution are the same. Then, any exchange will be essentially meaningless.

PE

 

[AgX]

Then, any exchange will be essentially meaningless.

But just the idea of variable contrast material made up of emulsions of different gradations necessitates the two respective sensitizers to stick at their grains,

 

[RauschenOderKorn]

But just the idea of variable contrast material made up of emulsions of different gradations necessitates the two respective sensitizers to stick at their grains,

An unsensitized emulsion and an orthochromatic should do the trick. Why would you use a second sensitizer?

 

[AgX]

Basically you are right, but both is done. (Spectral sensitizing is also applied just to gain speed.)
The issue of sensitizer relocation would remain anway.