B&W Reversal: thiourea as fogging developer?

[Raghu Kuvempunagar]

@Raghu Kuvempunagar - do you adjust first developer time if using thiourea as a nucleating agent instead of as a fogging developer?

I didn't have to but I've tried only on Kodak Double X and the previous generation Orwo UN54. You may need to adjust the acidity and duration of nucleating bath for your film. The less acidic the nucleating bath the warmer the positives as more silver sulphide specks are formed. Try first on non critical film with exactly the same steps as your tested process except for the light exposure which is now replaced by the nucleating bath.

 

[pkr1979]

I didn't have to but I've tried only on Kodak Double X and the previous generation Orwo UN54. You may need to adjust the acidity and duration of nucleating bath for your film. The less acidic the nucleating bath the warmer the positives as more silver sulphide specks are formed. Try first on non critical film with exactly the same steps as your tested process except for the light exposure which is now replaced by the nucleating bath.

Thanks! It is instead of a fogging developer though

 

[Raghu Kuvempunagar]

Thanks! It is instead of a fogging developer though

Just as one would use a normal second developer after light exposure, here also one would do the same. Only light exposure is replaced by the nucleating bath. Hope this is clear

 

[pkr1979]

Just as one would use a normal second developer after light exposure, here also one would do the same. Only light exposure is replaced by the nucleating bath. Hope this is clear

Crystal clear - thanks man

 

[pkr1979]

Today I tried using thiourea as a nucleating agent (if that is the correct term) prior to the second developer instead of as a fogging developer.

Meaning, instead of First Developer - Bleach - Clearing - Thiourea Fogging Developer,
I did First Developer - Bleach - Clearing - Thiourea Reversal Bath - Second Developer - Fix.

The parts that are the same I kept the same, meaning I exposed Ferrania Orto 50 at 32-40 ISO, First Developer was 14 minutes with 2.5g/L Thiocyanate. This produces good slides with thiourea as a fogging developer, but when replacing that with thiourea reversal bath, second developer and fix the slides are too thin and too low contrast (bright highlights but grey blacks). The tone is neutral.

I'll try this again by lowering First Developer time, amount of Thiocyanate, or increasing ISO. But before I do this - @Raghu Kuvempunagar - I did the thiourea reversal bath for 5 minutes instead of the 3 minutes you have suggested. Do you know if that might also be a factor in addition to First Developer times causing the positives to be to thin+low contrast? And, if I want slightly(!) warmer slides, can this be achieved by reducing the amount of acetic acid in the thiourea reversal bath?

 

[Raghu Kuvempunagar]

You can reduce acetic acid to get more warmth. I think I mentioned this in one of my previous posts - "the less acidic the nucleating bath the warmer the positives as more silver sulphide specks are formed." By reducing the amount of acetic acid used, you can make the bath less acidic.

Before you do further changes to your process such as thiocyanate concentration in FD, FD development time, etc. you can perhaps do a simple test. Take a piece of unexposed film, put it in the nucleating bath for 2-3 minutes, develop and fix. Check the result. Ideally it will be very dense blocking most of the light when you hold it against a light source. OTOH if it is too thin, then no change in the earlier steps of reversal process can give you good blacks. Also, this test will give you an idea of the dark tones that are possible if you repeat the test with varying concentration of acetic acid.

Nucleating bath shouldn't be longer than necessary as there is the risk of losing some halides due to the formation of soluble Thiourea-silver halide complexes. I suggest keeping the nucleating bath to 2-3 minutes.

 

[pkr1979]

You can reduce acetic acid to get more warmth. I think I mentioned this in one of my previous posts - "the less acidic the nucleating bath the warmer the positives as more silver sulphide specks are formed." By reducing the amount of acetic acid used, you can make the bath less acidic.

Before you do further changes to your process such as thiocyanate concentration in FD, FD development time, etc. you can perhaps do a simple test. Take a piece of unexposed film, put it in the nucleating bath for 2-3 minutes, develop and fix. Check the result. Ideally it will be very dense blocking most of the light when you hold it against a light source. OTOH if it is too thin, then no change in the earlier steps of reversal process can give you good blacks. Also, this test will give you an idea of the dark tones that are possible if you repeat the test with varying concentration of acetic acid.

Nucleating bath shouldn't be longer than necessary as there is the risk of losing some halides due to the formation of soluble Thiourea-silver halide complexes. I suggest keeping the nucleating bath to 2-3 minutes.

Will do - thanks.

 

[Raghu Kuvempunagar]

Related work which discusses a nucleating bath made using 1000 ml of water, 5 ml of glacial acetic acid and 0.4 g of thiosinamine (allyl thiourea):

https://patentimages.storage.googleapis.com/98/2a/7d/5da04d284f56f6/US2159466.pdf

Quoting from the patent:

"Suitable odorless sulfur compounds for producing silver sulfide nuclei are, for example, thiourea and its derivatives"

"The process is suitable for the reversal development of any black-and-white or color picture"

"These acid baths have further the great advantage of a much Ionger duration than the hitherto known neutral or alkaline baths. The nature of the acid used is without importance; its pH-value being alone decisive."

 

[pkr1979]

Related work which discusses a nucleating bath made using 1000 ml of water, 5 ml of glacial acetic acid and 0.4 g of thiosinamine (allyl thiourea):

https://patentimages.storage.googleapis.com/98/2a/7d/5da04d284f56f6/US2159466.pdf

Quoting from the patent:

"Suitable odorless sulfur compounds for producing silver sulfide nuclei are, for example, thiourea and its derivatives"

"The process is suitable for the reversal development of any black-and-white or color picture"

"These acid baths have further the great advantage of a much Ionger duration than the hitherto known neutral or alkaline baths. The nature of the acid used is without importance; its pH-value being alone decisive."

Thanks for this.

 

[pkr1979]

Im not getting proper results when using thiourea as a nucleating agent and I am hoping for some advise. I lowered FD time from 14 to 10 minutes, and thiocyanate from 2.5 to 2 g/L. But results are similar:

Notice also that the top part is darker than the bottom part. Any advise?

@Raghu Kuvempunagar - how are you using/mixing dithionite for reversal? Im considering to mix something up myself instead of IronOut.

 

[Raghu Kuvempunagar]

Not really sure if this going to solve any of the problems you're facing, but since you asked for my formula, here it is: 5 g Dithionite + 5 g Sodium Carbonate + 500 ml water. It should be used immediately after mixing, redevelop for about 10 minutes with sufficient agitation (initial 30 seconds continuous agitation followed by 2-3 inversions every minute thereafter).

@grainyvision who tinkered with Dithionite a lot more than me suggested another formula for fogging redeveloper: 1 tablespoon of ascorbic acid, 2 tablespoons of baking soda, and 2 tablespoons of iron out. I haven't tried this formula and not sure if it will solve your problems, but sharing with you for your reference.

The top-part darker than bottom-part issue is probably a processing error.

 

[pkr1979]

Not really sure if this going to solve any of the problems you're facing, but since you asked for my formula, here it is: 5 g Dithionite + 5 g Sodium Carbonate + 500 ml water. It should be used immediately after mixing, redevelop for about 10 minutes with sufficient agitation (initial 30 seconds continuous agitation followed by 2-3 inversions every minute thereafter).

@grainyvision who tinkered with Dithionite a lot more than me suggested another formula for fogging redeveloper: 1 tablespoon of ascorbic acid, 2 tablespoons of baking soda, and 2 tablespoons of iron out. I haven't tried this formula and not sure if it will solve your problems, but sharing with you for your reference.

The top-part darker than bottom-part issue is probably a processing error.

Thanks again for your help - much appreciated. Its probably not solving the issue regarding using thiourea as a nucleating agent. But Im not sure how much more I will be experimenting when IronOut and thiourea fogging developer works just fine. But Im curious to see if I can leave out fixing if I mix dithionite myself instead of using IronOut. IronOut does give good results though as long as I fix. The results are also good when using thiourea as a fogging developer. You are probably right about the top-part being darker then the bottom-part being a processing error - I just haven't experienced it before.

 

[Raghu Kuvempunagar]

Im curious to see if I can leave out fixing if I mix dithionite myself instead of using IronOut. IronOut does give good results though as long as I fix.

If you saw the reddit link I shared in my previous post, @grainyvision seems to have got good result with Iron out without needing to fix. So I take claims that fixing is necessary to get clear highlights and good contrast with a little bit of scepticism.The issue that you are facing with IronOut might be due to inadequate development of highlights in the first developer. Have you tried developing a little longer than your standard development time and/or increasing the amount of thiocyanate in FD by a small amount?

 

[pkr1979]

If you saw the reddit link I shared in my previous post, @grainyvision seems to have got good result with Iron out without needing to fix. So I take claims that fixing is necessary to get clear highlights and good contrast with a little bit of scepticism.The issue that you are facing with IronOut might be due to inadequate development of highlights in the first developer. Have you tried developing a little longer than your standard development time and/or increasing the amount of thiocyanate in FD by a small amount?

Thanks - yes, I saw the reddit link I have developer with longer FD time, more thiocyanate and both - but all of that is overkill. I'll try increasing agitation with Iron Out and see where that takes me - and maybe time as well. More like you do - Ive been agitating 4 times initially and 4 times half way (total time 6 minutes).

 

[Raghu Kuvempunagar]

Thanks - yes, I saw the reddit link I have developer with longer FD time, more thiocyanate and both - but all of that is overkill. I'll try increasing agitation with Iron Out and see where that takes me - and maybe time as well. More like you do - Ive been agitating 4 times initially and 4 times half way (total time 6 minutes).

You might also want to try @grainyvision's redeveloper and see if it fares any better.

 

[pkr1979]

You might also want to try @grainyvision's redeveloper and see if it fares any better.

Absolutely - its readily available chemicals as well.