Black and White Films With Two Emulsions

[Andrew O'Neill]

I've been using HP5-Plus for many years, and I've heard that it, like many 400 speed films, has two emulsions. A fast emulsion and a slow emulsion. What is not clear to me is are the two emulsions separate coatings, or are they combined, and coated as a single layer? I've heard that Bergger Pancro 400 has two emulsion... one consisting of silver nitrate, the other of silver iodide. Are they also mixed together or laid down separately? Does anyone know if HP5 uses both silver nitrate and silver iodide? Thank you!

andy

 

[Focomatter]

According to a diagram in the Pancro 400 instructions pdf there are two sensitivity layers as well as a bunch of others. Text cut and paste (top to bottom): Protective layer, High-sensitivity layer,
Low-sensitive layer, Anti-halation layer, Film base, Anti-curling layer

 

[Andrew O'Neill]

@Focomatter thanks for that. I'll stick that image here of Bergger Pancro 400's layers... So, it looks like they are laid down as separate layers. I'm curious about HP5, and other 400 speed (conventional) films. I imagine then that HP5's layers are also laid down separately...

 

[Focomatter]

What I find interesting is that the high sensitivity layer is on top of the low. Maybe whatever attenuation (shading) that exists is not significant.

 

[Andrew O'Neill]

What I find interesting is that the high sensitivity layer is on top of the low. Maybe whatever attenuation (shading) that exists is not significant.

It must matter. I'm sure it would have been tested. I wonder which layer is made up of silver iodide...
Maybe @Henning Serger and @Lachlan Young can shed more light on this, as well as HP5 and other 400 speed films.

 

[DREW WILEY]

There have been a number of dual ingredient films, not all of them fast, and not necessarily dual-layer. I've never heard of HP5 in that classification. I seem to recall that the now-extinct Fortepan 400 was a dual-layer film; I tried it once and wasn't exactly thrilled.

 

[Andrew O'Neill]

There have been a number of dual ingredient films, not all of them fast, and not necessarily dual-layer. I've never heard of HP5 in that classification. I seem to recall that the now-extinct Fortepan 400 was a dual-layer film; I tried it once and wasn't exactly thrilled.

Fuji Acros is apparently a mixed emulsion of two different grain types.

I thought HP5 was also made up with two grain types...One fast one slow. Mixed together in the same emulsion, I do not know... and what type of salt? Bromide? Iodide?

 

[DREW WILEY]

You'd have to ask Ilford. I don't think things can be classified quite that simply anyway, even if a manufacturer is willing to give away their emulsion secrets. I don't see why HP5 would be mixed grain, since it's a traditional long-toe film with a semi-thick emulsion. But I could be wrong.

Not so long ago I experimentally developed a particular medium speed film in an out-of bounds developer, and it visually came out with two distinctly different grain sizes, something I never noticed before. It ruined the image for fine printing purposes, but got me wondering. Sometimes when they do indicate a special coating procedure, it's has a marketing implication.

Films like Super XX and Bergger 200 had a very long scale based on just a single emulsion, as well as newer technology T-grain options like TMax.

 

[Andrew O'Neill]

Thanks Drew.

 

[MattKing]

I posted something about this about 1.5 years ago. It came from an extremely reliable contact in the film industry:

"Essentially, all black and white films since the very early days of film manufacture are “two-emulsion”, or more, films. In order to obtain films with speeds fast enough for indoor photography, films required multiple sized grains and for a film to become panchromatic, that meant that grains of different sizes would require dying to record red, green or blue light. Each of those dyed grain “sets”, in their own emulsion could then be mixed into one large emulsion to coat or split up to coat in several layers.

Another means of making a “two-emulsion” black and white film would be to split the grain sizes into small to mid-sized and mid-sized to large each set to its own emulsion, and mixing all three dyed silver grains together for a slow-to-mid and a mid-to-fast emulsion. All panchromatic black and white films manufactured for still film photography have been manufactured like this for a very long time, perhaps 40 years or more.

Why?

Separating the grain sizes gives the advantage for the film manufacture to better control the film speed when the emulsions are made, and also when they are coated. Light absorbing dyes can be added to optimize a specific region of the DlogE curve’s speed by dying the specific emulsion, which will lead to better consistency and linearity in the product. These are tools that the manufacturer would not have if all the speeds were coated “all as one”."

 

[Andrew O'Neill]

Interesting. Thank you, Matt. I imagine then that HP5 has duo emulsions with varying grain sizes but the question remains, are they combined into one or laid down as two, like Bergger Pancro 400. I appreciate Bergger sharing this aspect publicly.

 

[MattKing]

The modern Kodak emulsions are applied in separate layers when necessary, and mixed and applied as one when they can be. It is an issue of differing viscosities and tendency to mix well, and how that affects how things coat, not an issue of sensitometry or chemistry per se.
Harman's coating line is also modern, and while there are differences in the equipment, the principles are likely to be similar.
Kodak of course uses equipment and techniques whose main application is colour film, not black and white, and the approach with colour involves considerably more complexity as a result.

 

[lamerko]

ОRWO P400

 

[koraks]

I thought HP5 was also made up with two grain types...One fast one slow. Mixed together in the same emulsion, I do not know... and what type of salt? Bromide? Iodide?

'Grain type' is a problematic term as it smashes a number of parameters all into one, such as:
* Main chemical composition - film mostly uses silver bromide with a small fraction silver iodide
* Dopants, sensitizing dyes, acutance dyes etc. that are also part of the chemical makeup of the grain, or at least closely associated with it.
* Grain size
* Grain geometry/shape/aspect ratio
Probably some others, too.

When it comes to e.g. grain size and/or shape, they're not necessarily distinct, but generally within a certain bandwidth of a parameter. E.g. grain sizes ranging from x to y microns. So grain 'type' in itself is not necessarily clearly defined - or at least not universally so.

Then there's the distinction between coating layers and constituents of an emulsion. We often bunch it all together in the amateur domain, but there's of course a difference between one single coating layer that contains a mixture of different grain types vs. multiple coating layers, each with their own grain type(s).

It must matter. I'm sure it would have been tested. I wonder which layer is made up of silver iodide...

It's logical that the top layer would be the faster layer. You'd want to limit attenuation of incoming light for that layer, specifically. Putting a fast layer at the bottom is somewhat antithetic, especially in a monochrome film package.
I doubt any emulsion is pure silver iodide btw. I'd expect it to be a bromide-iodide mix; the ratio may very well differ, and as pointed out above, it's just one factor among many that affects emulsion performance.

Maybe @Lachlan Young could comment; if anyone is aware of Harman-specific emulsion makeups, it'd be him.

 

[halfaman]

The only company I recall doing single layer emulsions was the defunct Fotokemica and their Efke/Adox films, at least it was advertised like that. Rest are two layers at least with different types of grains, even films like TMax are a mix of a fast T-grain emulsion and a slow cubic grain emulsion.

 

[laser]

"Making KODAK Film 1st edition" has photomicrographs of the cross sections of Kodak B&W and color films. The light sensitive material in film is a combination of silver (Ag) halides AgCl, AgBr and AgI some times noted as AgX. The other silver halide made with Fluorine is not very light sensitive. Silver nitrate is not light sensitive; it is the material that contributes the silver (Ag) to the silver halide when the crystals are formed. One fact that is not discussed in the thread is that several emulsions makes are typically blended to create the material in a single layer. This allows fine tuning of the characteristics. The first edition of Making KODAK Film is available at:
www.makingKODAKfilm.com

 

[koraks]

@laser thanks for chiming in, but given your knowledge and experience on the matter, would you mind also commenting on the actual question at hand - i.e. the issue of several distinct coating layers in B&W materials?

 

[Milpool]

Interesting. Thank you, Matt. I imagine then that HP5 has duo emulsions with varying grain sizes but the question remains, are they combined into one or laid down as two, like Bergger Pancro 400. I appreciate Bergger sharing this aspect publicly.

If you ask Ilford/Harman they might answer specifically about HP5+.

I imagine it is similar to Tri-X which has two distinct layers, a fast layer on top of a slow layer. T-Max also has two distinct fast/slow layers (the top fast later being the tabular one). On the other hand I have a vague memory of an old article about Ilford Delta 100 in which that film was described as having a single (presumably mixed) layer. This may or may not have been correct so don't quote me on that.

Note that even if there are distinct layers they can often be coated at the same time (rather than in succession) using a multilayer slide/cascade curtain coater. I'd have to go back to Making Kodak Film (Robert Shanebrook) to check but if I remember correctly Kodak's slide coaters can do up to 10 layers at a time - which is especially important for colour films that have many layers.

 

[Andrew O'Neill]

Some very excellent info here, folks! For one, I had no idea that TMX consisted of a mixture of T-Grains and cubic grains.

 

[Andrew O'Neill]

I wonder if @Harman Tech Service could add anything to the discussion, especially in regards to HP5, and Delta 100...

 

[Andrew O'Neill]

ОRWO P400
View attachment 382943

Thanks, lamerko. I do believe I have a few 120 rolls in the freezer...

 

[MTGseattle]

Andy, are you headed down an interesting chemistry route?

Also, how long have film "curves" been available as a data point?

 

[Milpool]

Incidentally for anyone interested in the ins and outs of making film, Robert Shanebrook’s Making Kodak Film is a must-have reference. There are two editions - both great but the second one is greatly expanded.

Among other things there are cross section micrographs of various films showing the layers.

 

[John Wiegerink]

The very first film I ever tried in 1959 was Kodak Verichrome B&W in my little plastic Imperial Satellite 127 camera. Everybody always claimed it had two sensitivity layers also. I don't know, but it was a very forgiving film for beginners like me at the time. I can't remember for sure whether or not it was just called Verichome B&W or VerichomePan B&W at that time?
I was thinking like Focomatter in that the high sensitivity layer should be below the less sensitive layer? Just shows how smart I am when it comes to emulsion making!

 

[laser]

Incidentally for anyone interested in the ins and outs of making film, Robert Shanebrook’s Making Kodak Film is a must-have reference. There are two editions - both great but the second one is greatly expanded.

Among other things there are cross section micrographs of various films showing the layers.

Thanks for your kind comments.