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View Full Version : How to make the best emulsion, or why "Silver Rich" is a myth.



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dwross
02-23-2007, 12:19 PM
We shouldn't get lost in semantics and just admit that films prepared in different ways have a different look.

The same can be said of papers - and therein lies the art. Thank you for reinforcing an important concept to remember. Good science will get us a long way toward our goals, but at the end of the process, art will bring us home.

avandesande
02-23-2007, 12:39 PM
PE, I think 'admit' is not really what i was trying to say, 'recognize' is more appropriate.

Photo Engineer
02-23-2007, 02:18 PM
Oh, I agree. My main point is that with films, 'silver rich' is not the reason behind the look of the film. The reason comes from other factors than the amount of silver coated.

With paper, there is a small degree of coupling with the look and the amount of silver coated, but it is also related to the paper support. I will address that later, but maybe Denise might comment on her silver rich paper coatings for us.

PE

Alex Hawley
02-23-2007, 07:54 PM
We shouldn't get lost in semantics and just admit that films prepared in different ways have a different look.

Quite true Aaron. My observations were based on the look I am seeing. I had wondered why I was seeing such a difference with some of the papers I was trying. This thread jogged my mind as to what may be causing that difference.

I hope to run another set of paper comparisons this weekend when I try Ansco 130 for the first time. Reflecting back on this thread tonight, I thought of another variable, namely development time, that may be playing a factor towards what I am seeing.

Photo Engineer
02-23-2007, 08:22 PM
I decided to continue this part of the explanation here in the same thread.

Ok, why do things differ with paper? Well, if you look at a film curve it goes from dmin to dmax, and this dmax can vary from about a density value of 2.0 to 4.0. You can see this, and you can measure the silver quantity that is used to create the change in dmax and sometimes the contrast will change as well. As silver goes up, the highest possible dmax density of a given film goes up.

As silver level in paper is increased, once a density of about 2.2 is reached, no amount of silver will change the dmax that is measured, and what is seen changes very little. Contrast and speed will generally go up. (all of these assume glossy paper; with matte paper, the maxiumum density will fall to about 1.8)

However, if you view the dmax area of a paper print against a very bright light, a low silver paper will appear translucent to you and a silver rich paper will appear varying shades of gray or almost black. You will see little or no detail in the low silver paper, but you will see faint details in the high silver paper. By reflected light, both papers will appear to have the same dmax and measurments will show the same dmax in both, and the details in the high silver paper will vanish. Both papers have the same appearance to reflected light.

Now, what fools us all and complicates the situation is something called "Opacity". Opacity can be said to be the ability of a paper support to transmit light. Old time paper supports were very opaque due to thickness and whitening material such as baryta or titanox. Modern papers are thinner and allow more light through. Looked at under incident light, old and new papers may look the same, but by transmitted light there is more translucency to some modern papers.

In my example of dmax in papers above, I assumed that both the high and low silver papers had the same opacity. If opacity differs, then a high silver paper on a more translucent paper can look like a low silver paper in some tests especially where there is any ambient light coming from behind the paper.

So, a high silver paper can be subtly different, and more detail can be seen in dark areas if the paper is slightly backlit.

Now, here are some other factors to consider.

If the paper is low silver and high gelatin, the scatter can reduce sharpness, and if the paper is high silver and high gelatin, the scatter can be made to be similar to the low silver high gelatin paper and it will lose sharpness.

So, due to the reflection properties of paper, the situation with low and high silver becomes much more complex. In general, a high silver print will give you some faint indication of more detail, and will reveal it more and more with higher and higher levels of front illumination or a touch of back illumination depending on the 'opacity' of the paper itself.

As you can see, the silver level in paper is a different beast than silver level in film.

BTW, all modern films and papers have a very straight line mid portion of the curve, whatever the product, but older films had a distintive upwards bow in the center of the curve due to the different types of grain that were present in the emulsion. For the most part today, curve shape is controlled by grain size, not type, while in the past, curve shape was determined by both grain size and type.

This latter fact further changes the situation with respect to judgments about silver level. I have assumed throughout that a film or paper produces an equivalent curve in these comparisons. Such comparisons have been made, and I have seen many of them, particularly on reflection supports which was of particular interest to me.

The final answer seems to be that silver level does not affect film images much, but overall curve shape does. In paper, silver level can create a subjective impression that varies with support type and lighting.

PE

wirehead
02-24-2007, 01:07 PM
How does sub-surface scattering play in to this? Iwould imagine (I spent a bunch of time in college doing ray-tracing and computer graphics) that sometimes light can be reflected around the surface layer, especially from oblique angles.

Photo Engineer
02-24-2007, 01:16 PM
Sub-surface scattering reduces sharpness during exposure, and is dependant on layer thickness and amount and size of the silver grains. After processing, sub-surface scattering attenuates light and limits dmax, as explained above, to a value of about 1.8 for matte papers and about 2.2 for glossy papers.

Oblique or incident light will vary as a function of the surface of the paper, and can cause very unusual effects. I would not care to discuss it here. It takes a very sophisticated piece of equipment to measure the effects. That is called goniophotometry.

PE