Collodion Negatives: Copper Intensification Control

I've started making collodion negatives for salt printing. I expose them 1.5 to 2 stops more than positives, use a negative developer, and extend the development time. After developing and fixing, I use copper intensification.

While I know from Quinn Jacobson that copper intensification has limited control compared to pyro redevelopment, he also mentioned that some control is possible. How can I better control the density of my negatives using this process? I've also had success getting good contrast with this process, but I want to understand what kind of control I have.

For example, what's the difference in results when I vary the time in the **bleach solution** (Part A & B) , and the time in the **silver nitrate solution**?

I'm using this recipe from Giorgio Bordin:

**Bleach Solution**
* **Part A (20% solution):**
* Distilled water: 100ml
* Copper sulfate: 20g
* **Part B (10% solution):**
* Distilled water: 100ml
* Potassium bromide: 10g

**Intensifier (6% silver nitrate solution):**
* Distilled water: 200ml
* Silver nitrate: 12.5g
* Nitric acid: 3 drops

I haven't been adding nitric acid. What potential problems could this cause?

Thank you in advance!

The amount of time in the silver nitrate isn’t going to make much difference - the full intensification is complete in seconds - but shortening the time in the CuSO4 bath will have a big influence on how much density your negative builds in the silver bath.
Typically, the time in the copper bleach is recommended to be 60-90 seconds, but you can reduce that time to as little as 20 seconds and still get some intensification. But if you intend on using the negatives for processes like Salt printing, you’ll need plenty of density, so bear that in mind when you experiment with the bleach times.

retina_restoration said:

The amount of time in the silver nitrate isn’t going to make much difference - the full intensification is complete in seconds - but shortening the time in the CuSO4 bath will have a big influence on how much density your negative builds in the silver bath.
Typically, the time in the copper bleach is recommended to be 60-90 seconds, but you can reduce that time to as little as 20 seconds and still get some intensification. But if you intend on using the negatives for processes like Salt printing, you’ll need plenty of density, so bear that in mind when you experiment with the bleach times.

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Thank you very much for the detailed advice.

So if I understand correctly, a shorter time in the bleach results in lower density, while a longer time increases the density.


I’ve been trying for around 20–30 seconds and was able to achieve a certain amount of density. I’d like to test longer times—60 seconds or more—to see how that affects the appearance of salt prints.

Is there any detailed manual or reference that describes these processes?

If you know of one, I’d greatly appreciate it.

D_Quinn said:

Thank you very much for the detailed advice.

So if I understand correctly, a shorter time in the bleach results in lower density, while a longer time increases the density.


I’ve been trying for around 20–30 seconds and was able to achieve a certain amount of density. I’d like to test longer times—60 seconds or more—to see how that affects the appearance of salt prints.

Is there any detailed manual or reference that describes these processes?

If you know of one, I’d greatly appreciate it.

Click to expand...

It is generally recommended that the copper bleach bath be about 60 seconds for a hefty amount of intensification, sufficient for Salted Paper printing, which requires dense highlights. If you don't need densities like what Salted Paper requires, then you can certainly do shorter times in the bleach (it's the amount of bleaching you do that determines how much intensification you're going to get), but anything shorter than 20 seconds is likely going to be less than what you need for any alt print processes.

I have found that anything less than 30 seconds in the black will not give you enough intensification for Salted Paper print making. If you plan to print on silver gelatin paper, then you don't need to intensify the negative at all.

I'm aware of Quinn's technique for iodine + pyrogallol redevelopment to increase density on the negative, and I have used it a few times. But I found it insufficient compared to the copper bleach technique — I simply couldn't get enough density built up using his process, so I have gone back to using the copper bleach technique.

As for "a detailed manual", you can't go wrong with John Coffer's "Doer's Guide to Wet Plate Photography". (about halfway down the page) Yes, it's expensive, but it's the most thorough of the manuals and includes plenty of instruction on the making of negatives for salt prints, albumen prints, etc.

If you want a specific book for Salted Paper print-making, you can't do better than Christina Anderson's book.

@retina_restoration
Thank you very much for the detailed explanation. I’ll also take a closer look at the book you mentioned (I’ve tried redevelopment myself, but I also couldn’t get enough density). Coffer's manual seems very useful, but unfortunately, the manual isn’t shipped outside the U.S., which is a shame!

I’m planning to run some tests soon, combining density control with exposure.
For example, what kind of differences would you expect in a salted paper print between:

• a negative made with exposure on the more overexposed side (about 2.5 stops over a proper positive exposure) but with weaker intensification, and
• a negative made with less overexposure (about 1.5 stops over a proper positive exposure) but with stronger intensification?

D_Quinn said:

@retina_restoration
Thank you very much for the detailed explanation. I’ll also take a closer look at the book you mentioned (I’ve tried redevelopment myself, but I also couldn’t get enough density). Coffer's manual seems very useful, but unfortunately, the manual isn’t shipped outside the U.S., which is a shame!

I’m planning to run some tests soon, combining density control with exposure.
For example, what kind of differences would you expect in a salted paper print between:

• a negative made with exposure on the more overexposed side (about 2.5 stops over a proper positive exposure) but with weaker intensification, and
• a negative made with less overexposure (about 1.5 stops over a proper positive exposure) but with stronger intensification?

Click to expand...

I think these are questions that only you will be able to answer through testing. It seems you are looking to develop your own personal visual language for salt printing, and only testing a variety of approaches will tell you what you want to know.
Salt prints require an intense negative to work well, and anything less than this will likely yield flat results.

retina_restoration said:

I think these are questions that only you will be able to answer through testing. It seems you are looking to develop your own personal visual language for salt printing, and only testing a variety of approaches will tell you what you want to know.
Salt prints require an intense negative to work well, and anything less than this will likely yield flat results.

Click to expand...

Thanks for your advice. You’re right. I’m going to run some tests to see how copper intensification and slight overexposure (beyond what I’d normally use for positives) influence the look of salt prints.

@retina_restoration
One quick thing I’d like to confirm:
About the bleach solution, as I mentioned previously, I’ve been using Giorgio Bordin’s recipe, where I mix the following two solutions right before bleaching:

• Copper sulphate / water (80 g / 400 ml)
• Potassium bromide / water (40 g / 400 ml)

Then, in an article I happened to come across just a few days ago (Chapter-17-Wet-Plate-Collodion-Process.pdf, p.54), the working bleach is described like this:
“Stock Solution A: copper sulphate 18 g / 100 ml water.
Stock Solution B: potassium bromide 9 g / 100 ml water.
To make a working solution of bleach, take 7 ml of A and 7 ml of B, then add them to 300 ml of distilled water…”

From this, it seems that the working bleach solution in the PDF is much more diluted than Giorgio Bordin’s recipe, since the stock solutions are further diluted with water.

My question is: Are you using the same bleach solution as Bordin, or a different one?

And as always, thank you so much for your valuable advice!

I’m certain that the Bordin recipe you’re quoting is intended as a stock solution, not a working strength solution!

I use John Coffer’s recipe, which goes like this (quoting Will Dunniway’s document):

You cannot allow this plate to dry before the intensification is done. If you do, than the intensification cannot be done.

‘Mild’ Intensification Formula.
Taught to me by John Coffer

STOCK SOLUTION A
Distilled Water . . . . . . . 100 ml
Copper Sulfate . . . . . . . . 18 grams

STOCK SOLUTION B
Distilled Water . . . . . . . 100 ml
Potassium Bromide . . . . 9 gram

SILVER INTENSIFICATION SOLUTION

Distilled water . . . . . . . 200ml
Silver nitrate . . . . . . . . . 12 grams
Nitric Acid . . . . . . . . . .6 drops

Now mix 7 ml for each stock solutions A & B into 300 ml of distilled water. This is your bleach solution. Take the rinsed and fixed glass negative and place it into this newly mad bleach solution. Agitate slightly for around 20 seconds. If the chemical bleach is warm, than less time is required. If the chemical bleach is cold, than more time is required. As you see slight changes in the plate as it bleaches and within these time boundaries, pull the plate and place it into a tray of distilled water. Agitate for about one minute, Dump the water and add fresh distilled water to this same tray.
(I use running water for about 60 seconds, followed by a quick rinse with distilled water)

Rinse some more. Pour this silver solution into a clean tray. Now insert your bleached plate into this tray and with one even wave like motion, in the blink of an eye, flow this silver solution across your image. This intensification will blacken your plate’s images, taking only a few seconds. Quickly rinse. Let dry and varnish.

Thank you for your reply!
In Bordin’s video, it looks like he mixes the stock solutions directly without diluting them in water:

With this method, the density is strong enough, but the change happens so quickly that it’s difficult to control. That’s why I’d like to try the method you mentioned (Coffer’s way).

D_Quinn said:

Thank you for your reply!
In Bordin’s video, it looks like he mixes the stock solutions directly without diluting them in water:

With this method, the density is strong enough, but the change happens so quickly that it’s difficult to control. That’s why I’d like to try the method you mentioned (Coffer’s way).

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I can't imagine trying to control the process if you're using a bleach that strong. Most practitioners I know use the method I outlined, originally from John Coffer. If anyone knows what they're doing with Collodion, It's John.