Selenium (KRST) Intensifying A Negative To Increase Contrast

[Andrew O'Neill]

 

[pentaxuser]

Thanks, Andy. Two questions: What does the increase brought about by the selenium intensification equate to in terms of increase in contrast i.e. what increase in grade in terms of a print might this represent? I have heard that selenium might achieve a whole grade or more likely half a grade only

As selenium intensification of say a 35 or 645 neg requires much less liquid than an 8x10 then the amount of selenium required gives much less of an issue in terms of pungency and potential harm to the user? Would a partly opened window be enough?

pentaxuser

 

[Andrew O'Neill]

Thanks, Andy. Two questions: What does the increase brought about by the selenium intensification equate to in terms of increase in contrast i.e. what increase in grade in terms of a print might this represent? I have heard that selenium might achieve a whole grade or more likely half a grade only

As selenium intensification of say a 35 or 645 neg requires much less liquid than an 8x10 then the amount of selenium required gives much less of an issue in terms of pungency and potential harm to the user? Would a partly opened window be enough?

pentaxuser

It's the same as if I gave the film N+1 development, without the increase in B+F. If I print it on grade 1 paper, it's like printing on grade 2.
At the 1+3 dilution (I've used 1+2 but the fumes are quite strong) I use 150ml of stock to cover 120 in my Paterson tank. I also use this amount for doing sheet film in trays. It's quite a bit of stock if you intend to do an entire roll, so make sure you have sufficient airflow. If you are just doing a frame or two (cut from roll), then much stock will be required... In a 4x5 tray, only 50ml of stock is required.
I'm very cautious. I started wearing a respirator about 20 years ago (in enclosed space). When I started using this technique, I was living in Japan, and worked with a window opened (no respirator). I didn't have a proper darkroom, instead used a spare bedroom. There is nothing wrong with intensifying negatives outside, in fact, I used to tone prints this way (in Japan due to lack of space). Hard to do here, as it rains most of the time, this time of year.
You could dilute the stock even further (requiring less stock), and extend the intensifying time. I have not experimented with this, though... With weaker dilutions, it's harder to smell the selenium. I dilute selenium 1+100 when toning kallitype prints. Can't smell it.

 

[pentaxuser]

Thanks. Yes what I was thinking of, Andy, was just the odd negative which for some reason need a boost in contrast. In that case the amount of even strong selenium at 1+3 could be small and might not require any special precautions

I looked at the Ilford video on selenium toning a print to achieve a colour change and this involves 150ml of selenium at 1+3 so a lot of selenium and yet the demonstrator only wears gloves and goggles but no face mask although she stresses that it should be done in a well ventilated room. It was done in what looked to be a large room by normal home darkroom standards but it wasn't clear if the ventilation was by fans or simply by size of room with some form of ventilation. It wasn't even clear if this was by size of room only or size plus open windows or vented panels in the room allowing an exchange of air

This is a bit of a deviation but can I ask: Is a strong dilution, say 1+3or 4 simply a potential irritant that is largely harmless if used only occasionally or is there something in selenium that is harmful per se to the lungs and/or the internal organs of the body

pentaxuser

 

[JPD]

This is a bit of a deviation but can I ask: Is a strong dilution, say 1+3or 4 simply a potential irritant that is largely harmless if used only occasionally or is there something in selenium that is harmful per se to the lungs and/or the internal organs of the body

The smell is ammonia, which is an irritant.

 

[Andrew O'Neill]

What JPD said. Breathing the fumes in for long periods of time would be a no no. If one uses it occasionally (like me), then a room with decent airflow is sufficient.

 

[john_s]

Thanks. Yes what I was thinking of, Andy, was just the odd negative which for some reason need a boost in contrast. In that case the amount of even strong selenium at 1+3 could be small and might not require any special precautions

I looked at the Ilford video on selenium toning a print to achieve a colour change and this involves 150ml of selenium at 1+3 so a lot of selenium and yet the demonstrator only wears gloves and goggles but no face mask although she stresses that it should be done in a well ventilated room. It was done in what looked to be a large room by normal home darkroom standards but it wasn't clear if the ventilation was by fans or simply by size of room with some form of ventilation. It wasn't even clear if this was by size of room only or size plus open windows or vented panels in the room allowing an exchange of air

This is a bit of a deviation but can I ask: Is a strong dilution, say 1+3or 4 simply a potential irritant that is largely harmless if used only occasionally or is there something in selenium that is harmful per se to the lungs and/or the internal organs of the body

pentaxuser

KRST is basically alkaline fixer, with some S replaced by Se which is in the same group in the periodic table so is somewhat similar chemically. So probably no need to be more alarmed by KRST than by alkaline fixer.

 

[koraks]

or is there something in selenium that is harmful per se to the lungs and/or the internal organs of the body

Selenium is highly toxic and probably the most toxic compound commonly used in a home darkroom without people being aware of its toxicity. Part of what makes it nasty is that it's chemically very similar to sulfur, which is readily absorbed by the body and plays a role in several physiological processes. Selenium in toner doesn't fume or vaporize just like that, so handling solutions of selenium toner is mostly annoying because of the ammonia, not so much the selenium itself. However, this is in the assumption that gloves are worn, all utensils and surfaces the selenium comes into contact with are cleaned well and everything is done to prevent exposure to the actual selenium. This includes taking care to remove stains of selenium toner which will dry up and then may throw up a selenium-loaded dust if disturbed.

Practically speaking, selenium toner can be handled safely quite easily, but it's good to be aware of the precautions needed.

Speaking of safety and handling nasty stuff - I regularly use dichromate to intensify negatives. It's far more effective than selenium, especially because the process can be repeated as often as desired to build up the required density. Selenium toner is a single step; what density you get is the most you'll ever get since the negative can't be bleached back afterwards for further reprocessing.
Handling dichromate comes with much the same precautions as selenium, but contrary to selenium, virtually everybody knows damn well that dichromate is nasty stuff.

 

[pentaxuser]

Thanks all. I can recall the strong smell of ammonia in the 1950s when my parents were using whatever they were in connection with re-painting a room either cleaning home It certainly was an irritant to the lungs when used in a room

pentaxuser

 

[koraks]

Yes, ammonia is a very effective degreasing agent; we used it on our present home when we painted it the first time round. It used to be a smoker's house and the ammonia was indispensable in some spots to get the tar and nicotine off. But it's an irritant, for sure. The only 'advantage' is that humans are so sensitive to the smell of ammonia that they'll generally flee the area before things get properly dangerous.

 

[Doremus Scudder]

Replenished and reused KRST loses it's ammonia smell over time. I used to keep a 1+2 dilution of KRST just for intensifying negatives. The ammonia odor was much less after using it a few times. When I switched to PMK for most of my work, the selenium intensification didn't work as well and bleach/redevelop become a better alternative.

Doremus