POP vs DOP/visible vs latent - what's the chemical difference?

w.out said:

If I'm understanding this correctly, increasing the speed of DOP paper is not achieved by increasing the silver halide (which explains those 'silver rich is a myth' threads here on APUG), but by keeping the ratio of silver to salt stoichiometric and rather by including ingredients in the emulsion that increase the sensitivity of the halide, such as active gelatin, ammonia, etc. Am I on the right track with that?

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It is kind of ironic that the actual speed of the POP is greater than DOP if you define speed as the amount of amount of Silver metal formed per unit of exposure. However, since you need only a smidgen of exposure in DOP to form the latent image (the rest being finished in the developer,) the "effective" speed is greater. Kind of akin to a painter doing a Plein Air painting taking hours vs sketching the scene quickly and finishing the painting in the studio.

I am not familiar with the debate around the "silver-rich" myth. Perhaps you can point to a good thread or two on the subject.

I am also not well versed with the nitty-gritty of emulsion making as many on the thread/forum so I will leave to them to explain the minutia regarding the roles of ammonia, active gelatin etc. My best initial guess would be that all of these additives are used to affect the morphology (micro-structure) of the colloidal halide (size, shape, distribution etc) in the emulsion with the goal of making a more efficient use of the available photons during exposure. As a result, the emulsion becomes speedier overall. However, the halide itself does not become any more sensitive per se as it is governed only by the underlying photo-physics.

re "silver-rich"
The story is more nuanced than myth vs not-myth. Undoubtedly, some marketeers have used the term to imply superior quality. Marketeers tend to do those kinds of things. Judging this particular claim, however, comes down to an individual's personal definition of "quality."

Newer emulsion formulations are more conservative of silver than the old emulsions. More of the silver becomes active and the grains are flat/"tabular" (hence the name T-grain), as opposed to variations on cubic shapes. The photo-receptive T-grains lie in a more-or-less single layer. There can be fewer grains because most of their surface area faces the light and because they are inherently more sensitive (from both emulsion making technique and chemical additives). Their improvement in sharpness over the older emulsions was perceived as an advancement in photography. Today, with ever-increasing expectations for sharpness, even T-grain films can seem soft compared to digital. This leads to statements such that Weston's famous pepper, a contact print from a large negative, is "soft" and "nothing special." Tastes change.

The older emulsion formulations do indeed have more silver in them. They have to. A proportion of the silver grains are what is termed "dead." They are inactive. They just sit there in the gelatin matrix (thicker than that of modern films). But, they sit there reflecting light. Not dead at all. They are part of the look of the old films and papers. There is a glow to them. If you like the glow and the subtle softness from more individual grains in a thicker coating, which together impart an almost 3D feel to an image, then "silver rich" is a meaningful term.

nmp said:

It is kind of ironic that the actual speed of the POP is greater than DOP if you define speed as the amount of amount of Silver metal formed per unit of exposure. However, since you need only a smidgen of exposure in DOP to form the latent image (the rest being finished in the developer,) the "effective" speed is greater. Kind of akin to a painter doing a Plein Air painting taking hours vs sketching the scene quickly and finishing the painting in the studio.

I am not familiar with the debate around the "silver-rich" myth. Perhaps you can point to a good thread or two on the subject.

I am also not well versed with the nitty-gritty of emulsion making as many on the thread/forum so I will leave to them to explain the minutia regarding the roles of ammonia, active gelatin etc. My best initial guess would be that all of these additives are used to affect the morphology (micro-structure) of the colloidal halide (size, shape, distribution etc) in the emulsion with the goal of making a more efficient use of the available photons during exposure. As a result, the emulsion becomes speedier overall. However, the halide itself does not become any more sensitive per se as it is governed only by the underlying photo-physics.

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(there was a url link here which no longer exists) is the one I was talking about. A lot of it went over my head, but between what you've said and what's said in there, I have a handle on the concepts at least. Thanks again.

dwross said:

re "silver-rich"
The story is more nuanced than myth vs not-myth. Undoubtedly, some marketeers have used the term to imply superior quality. Marketeers tend to do those kinds of things. Judging this particular claim, however, comes down to an individual's personal definition of "quality."

Newer emulsion formulations are more conservative of silver than the old emulsions. More of the silver becomes active and the grains are flat/"tabular" (hence the name T-grain), as opposed to variations on cubic shapes. The photo-receptive T-grains lie in a more-or-less single layer. There can be fewer grains because most of their surface area faces the light and because they are inherently more sensitive (from both emulsion making technique and chemical additives). Their improvement in sharpness over the older emulsions was perceived as an advancement in photography. Today, with ever-increasing expectations for sharpness, even T-grain films can seem soft compared to digital. This leads to statements such that Weston's famous pepper, a contact print from a large negative, is "soft" and "nothing special." Tastes change.

The older emulsion formulations do indeed have more silver in them. They have to. A proportion of the silver grains are what is termed "dead." They are inactive. They just sit there in the gelatin matrix (thicker than that of modern films). But, they sit there reflecting light. Not dead at all. They are part of the look of the old films and papers. There is a glow to them. If you like the glow and the subtle softness from more individual grains in a thicker coating, which together impart an almost 3D feel to an image, then "silver rich" is a meaningful term.

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Succinct. If there was a like button I would like this.

Is the silver nitrate I buy from Local Dark Room Supplies Store more active and tabular than what Ye Old Photographers were using, or are you saying that today's industrial manufacturers have access to better silver than anyone from the past?

w.out said:

Succinct. If there was a like button I would like this.

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I second that, (thanks dwross, you have a wonderful website by the way.) I learned something new from that post and the thread you linked to. As usual the truth is somewhere in the shaded area between black and white.

w.out said:

Is the silver nitrate I buy from Local Dark Room Supplies Store more active and tabular than what Ye Old Photographers were using, or are you saying that today's industrial manufacturers have access to better silver than anyone from the past?

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No, not the silver nitrate. That come in either crystalline form that you make a solution out of or as pre-made solution. That has not changed. It is what happens after that, i.e. when the nitrate solution meets the salt solution to make silver halide which is insoluble in water so it comes out of the solution (white precipitates that you see when making an emulsion.) It is the nature of those silver halide crystals/grains is what we are talking about. Depending on how you make them, the shape, size and distribution all change and so does the optical property of the end product. Just like you can get nice fluffy snow flakes to golf ball size hail all depending on how the cold air meets the moisture in the clouds.

The tabular shape (specifically round) has the highest surface area for a given volume (mass) - the reason why the nature made the red blood cells in the shape of circular platelets for facilitating more efficient absorption of oxygen in the lungs. Obviously then this type of shape will be better at catching the incoming radiation and covert to silver metal, particularly if you can orient them all flat in a plane. One can also expect that Dmax of the resulting developed image will be higher than in a film/paper of same overall silver loading with spherical or cubical shapes. Or conversely one can use lower loading with tabular shaped grains than the other shapes to achieve the same final Dmax. Probably that was the impetus for developing a process that gave the tabular shaped silver halides. Less "silver-rich" but better or comparable end result.

Probably off-topic, but many processes form a visable latent image, yet are DOPs, such as Platinum and Palladium printing. One gets the best of both worlds: The self-masking of the POP and the speed of the DOP.

Vaughn said:

Probably off-topic, but many processes form a visable latent image, yet are DOPs, such as Platinum and Palladium printing. One gets the best of both worlds: The self-masking of the POP and the speed of the DOP.

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Ziatypes are yet POPpier than the plain Pt/Pd.

w.out said:

Is the silver nitrate I buy from Local Dark Room Supplies Store more active and tabular than what Ye Old Photographers were using, or are you saying that today's industrial manufacturers have access to better silver than anyone from the past?

Click to expand...

NO it has nothing to do with the silver nitrate. The term "tabular" has to do with the appearance of the silver halide particles in an emulsion.

https://en.wikipedia.org/wiki/Tabular-grain_film

http://cool.conservation-us.org/coo...itale/2007-04-vitale-filmgrain_resolution.pdf

nmp said:

Ziatypes are yet POPpier than the plain Pt/Pd.

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Think I'll stay with the standard Pt/pd -- though I do have some negatives that would benefit from the lower contrast control the Ziatypes have.