Emulsion thickness

[rai]

Greetings! Could someone tell me the thickness of the ideal photographic emulsion to make photographic film? Thank you!

 

[dE fENDER]

0 mm to fully prevent light ray diffusion.

 

[Donald Qualls]

From a real world standpoint, 120 film is about .004" (appr. .01mm) thick, including base, any back side coatings, undercoat, AHU, emulsion, and overcoats (scratch protection etc.). I'm guessing, but the plastic base is probably at least half of that, it not three fourths, giving about .001" to .002" (.0025 to .0050 mm) to account for all the coatings on both sides of the base. And don't forget, with color film there are at least three color layers, a filter layer, and likely some intermediate layers in the portion lumped together as "emulsion".

In other words, commercially coated emulsion layers are Pretty Danged Thin.

Fortunately, DIY emulsion need not be anything like that thin unless you have a need to make 24x36mm or smaller image frames produce high quality images.

 

[rai]

Thanks!

 

[removed account4]

hi rai
have you been to Denise ross's site the light ( http://thelightfarm.com )
Denise also has a book on making emulsion ( https://www.blurb.com/b/6465389-the-light-farm ) ...
she has coated her own film and gives insights on how much emulsion you will need, its much more than 0 mm
I coats some paper today with hand made emulsion, I did 3 coats...

have fun !
John

 

[rai]

OK, I will walk the web!

 

[MattKing]

I just looked through my copy of Bob Shanebrook's "Making Kodak Film" - first edition.
The photomicrographs he includes on page 7 which show cross sections don't supply dimensions, other than 125 microns for the acetate support, although the indicator for scale makes me think that the various emulsion layers of a 400 TMax film are in total about 15 μm thick.
Perhaps you could start a Conversation here with Bob - his Photrio handle is laser.

 

[Lachlan Young]

Agfapan APX 25 was publically spec'd at 3 micron, APX 100 at 7 micron, APX 400 at 10 micron for the total coated thickness of all layers when dry. I recall many colour neg films are in the 15-25 micron range, colour transparency in the 20-30 microns range for total coated thickness when dry. This may differ between manufacturers to some extent, but probably not dramatically so - especially among those who use waterfall/ slide coatings.

 

[RogerHyam]

The Zone System (with N+ and N- dev) is predicated on the use of thicker emulsions from earlier in the 20th century and doesn't work as well with more modern thin emulsions. Personally I don't feel I can alter the contrast of HP5+ very much by push/pulling but Fomapan 100 (which I presume is an older, thicker emulsion) responds quite well - but is probably not such a good general purpose film.

Contrast control is really noticeable doing dev by inspection on my own emulsion which I presume are as thick as 19th Century emulsions i.e. about 1/2 inch.

These are the fog and ISO tests from my last batch. The top neg was over exposed and under developed the other was under exposed over developed (about 2 stops). You wouldn't get such a contrast change from a modern thin emulsion.



So if you want contrast control, perhaps to produce negatives suitable for historic print techniques, then thicker emulsions may be "ideal".

I expect someone more knowledgeable will say this has nothing to do with physical emulsion thickness now! There are obviously other factors involved as well as physical thickness.

 

[Lachlan Young]

The Zone System (with N+ and N- dev) is predicated on the use of thicker emulsions from earlier in the 20th century and doesn't work as well with more modern thin emulsions. Personally I don't feel I can alter the contrast of HP5+ very much by push/pulling but Fomapan 100 (which I presume is an older, thicker emulsion) responds quite well - but is probably not such a good general purpose film.

Contrast control is really noticeable doing dev by inspection on my own emulsion which I presume are as thick as 19th Century emulsions i.e. about 1/2 inch.

These are the fog and ISO tests from my last batch. The top neg was over exposed and under developed the other was under exposed over developed (about 2 stops). You wouldn't get such a contrast change from a modern thin emulsion.

View attachment 257421

So if you want contrast control, perhaps to produce negatives suitable for historic print techniques, then thicker emulsions may be "ideal".

I expect someone more knowledgeable will say this has nothing to do with physical emulsion thickness now! There are obviously other factors involved as well as physical thickness.

It's not necessarily emulsion thickness, but number of emulsions - many older materials were a single, relatively polydisperse emulsion, while most modern materials use multiple much more monodisperse/ high aspect ratio/ epitaxial emulsions to get a better speed/ grain/ sharpness balance. As soon as you get multiple emulsions, they can begin to diverge in development rate, especially if severely underdeveloped, creating problems in the straight line etc. There are huge numbers of problems (internal reflection, turbidity etc - and that's before considering the sensitometric/ potentially lumpy curve shape issues) with the older polydisperse emulsion designs - which is why they were got rid of. That said, many sub 100 speed single emulsion films were not dramatically different in dried thickness to today's films, and the fastest single layer ones were probably not dramatically different in total thickness to today's 2-layer 400 speed BW films. And the very old wet plate methods produced a very thin sensitised layer - which is why they're so sharp - turbidity is a major problem that afflicts gelatin emulsions as they get thicker.

HP5+ is very amenable to contrast control, though a lot depends on what developer you are using - too often people don't realise that some developers either run out of steam very fast at some dilutions, or that you can switch to something much more aggressive (PQ Universal) to stretch things further. With multigrade papers, you shouldn't need to excessively reduce development time - and indeed, too much N- can flatten midtones badly - in those cases, unsharp masking/ over threshold fogging to deal with getting highlights into range can deliver better results, precisely because you can keep a better midtone gradient. Kodak make pretty strong hints that you really shouldn't take T-Max films below a contrast index of 0.5-0.6 - so that you don't mess up the multiple emulsion relationships - and/ or make the films painful to print - they have such a long straight line into the highlights at that CI anyway, that you can just burn them in & keep good gradation - as opposed to films that shoulder the highlights, which gives you muddier tonal separation if you go to burn in.

 

[138S]

Greetings! Could someone tell me the thickness of the ideal photographic emulsion to make photographic film? Thank you!

To make DIY film and plates, with recipes around, you coat a 0.25mm to 0.5mm layer of melted emulsion. Once water is evaporated the final thichness may be 1/10 of the original layer, depending on the water content.

Industrially made film is a way different thing, their refined coating systems allow other parameters.

Of course The Light Farm is a great source. Also see this introduction, it tells a dose for a plate.

https://unblinkingeye.com/AAPG/DPlate/dplate.html

 

[RogerHyam]

I told you someone would have a better explanation! Thanks Lachlan. I've not tried HP5+ in PQ - maybe I should.

 

[Lachlan Young]

I told you someone would have a better explanation! Thanks Lachlan. I've not tried HP5+ in PQ - maybe I should.

Something else to consider with handcoated emulsions is that without a supercoat they will often develop dramatically faster than manufactured emulsions - the supercoat doesn't just protect the emulsion, it can regulate the diffusion rate of chemistry etc. Specific emulsion grain shapes (available surface area essentially) can develop much faster than others - T-Max 100 is on the record as having a thicker supercoat to regulate its development rate.

Are you trying to get N+ from HP5+ for silver or non-silver processes? You might be surprised how far ID-11 goes - if used full strength. I've managed to stretch a flat scene on to G2 with no issues without exceeding ID-11's abilities.

 

[RogerHyam]

During lockdown I did some experimenting with Ilfotec HC 1+1 making negs for Argyrotype and Cyanotype and had more join with Fomapan that HP5+ (my default film) but it isn't a priority now that I've fallen down the rabbit hole of making my own emulsions.

 

[Lachlan Young]

Ilfotec HC

Although purely anecdotal (& not having the urge to do a lengthy sensitometric investigation into this), I have noticed that whenever contrast issues with HP5+ crop up, it almost always seems to involve HC or HC-110.

 

[Nodda Duma]

Something else to consider with handcoated emulsions is that without a supercoat they will often develop dramatically faster than manufactured emulsions - the supercoat doesn't just protect the emulsion, it can regulate the diffusion rate of chemistry etc. Specific emulsion grain shapes (available surface area essentially) can develop much faster than others - T-Max 100 is on the record as having a thicker supercoat to regulate its development rate.

Are you trying to get N+ from HP5+ for silver or non-silver processes? You might be surprised how far ID-11 goes - if used full strength. I've managed to stretch a flat scene on to G2 with no issues without exceeding ID-11's abilities.

That’s not necessarily true. Handcoated emulsions typically develop out at same rate or longer than modern emulsions.

-Jason

 

[Lachlan Young]

That’s not necessarily true. Handcoated emulsions typically develop out at same rate or longer than modern emulsions.

-Jason

Reviewing my notes, I'd agree. It'll likely have a lot to do with the characteristics/ shapes of the grain - and the substrate used. Japanese paper was the stuff that seems to be very fast indeed.

 

[dwross]

Reviewing my notes, I'd agree. It'll likely have a lot to do with the characteristics/ shapes of the grain - and the substrate used. Japanese paper was the stuff that seems to be very fast indeed.

Thin paper allows the developer to reach the emulsion from both sides. That's usually not quite double the developing speed of emulsion on glass or film. Handcoated emulsions tend to develop out just a bit slower than modern commercial emulsions because they're usually coated a little thicker -- a good thing, in my opinion. The characteristics that we value in the old emulsion formulas is in part due to the thicker coating.

My guide for coating thickness is fixing speed. Your emulsion should clear in only a little more time than recommended for commercial materials. Just as important is that a plate clear at the same rate across the whole plate.

 

[Lachlan Young]

Thin paper allows the developer to reach the emulsion from both sides.

That's what seemed to be happening - thanks for the confirmation.