Thornton Two Bath & contrast control

[Alex Benjamin]

For those who use TTB regularly but don't have Thornton's book Edge of Darkness, there are some interesting notes in there on contrast control when using the developer. I find them useful, as, with the heat of summer, I've noticed a slight increase in contrast (albeit with no blown highlights) with HP5+ @ ISO250 with the devevloper at 24ºC when doing my normal 5 minute time in each baths.

Here's what Thornton wrote after giving the formula :

"You can fine tune the contrast of your negatives with this formula by increasing or decreasing the amount of Sodium Metaborate in the second bath between about 7 and 20 grams [note: formula asks for 12 grams in 1 litre]. In fact, you can get a kind of Zone system development control by having three different Bath Bs mixed — on each of 7, 12 and 20 grams content to handle very high, average, or very low subject brithness range respectively. [...]

Incidentally, Bath A, without an alkali activator, lasts a long long time in a well sealed bottle — much longer than conventional developer. A year is not uncommon. All that happens is that a small amount is absorbed by each film, developer, and the volume is slightly decreased each time of use. Replenishment is unnecessary. 15 films per litre are easily developed before replacement. Bath B discolors because of oxidised traces of Bath A in it, but this does not reduce its effectiveness. Again 15 films per litre are easily achieved."

This, I believe, corrects some opinions regarding the effectiveness of Bath B after a few films stated in the thread started by @What About Bob here.

 

[bags27]

Thanks. I used Thornton's 2 bath for a couple of years (no problems: just tended more toward Pyrocat HD) and never had a problem with B after many uses.

Edge of Darkness is a truly wonderful book!

 

[john_s]

Some thoughtful comments from an experienced user of Thornton's Two Bath here:

Effects of increasing Sodium Metaborate in BTTB

In general may I know what effect it will incur on the contrast when I increase the Sodium Metaborate say from 12g to 15g. My plan is to have slightly higher action Bath B(close to 20g, for winter) and cut back the development time for normal contrast to hight contrast scenes.

www.photrio.com

 

[What About Bob]

Thanks Alex and John. I need to get my hands on this book. This stuff is great, isn't it?

I really like the results from using the 20 grams per liter. The look is crisp and clean. The images look sort of like those black and whites from the 50s.

When I add Bath B in the tank I let it rest for one minute and do one very slow twist every minute. I was thinking of doing only one slow inversion at the halfway point and then just leave the tank alone for the rest of the time.

Now that I have potassium carbonate that I got for making D-72, Dektol, this will be fun to play with for Bath B. Use this for flat scenes.

 

[john_s]

.........................................

Now that I have potassium carbonate that I got for making D-72, Dektol, this will be fun to play with for Bath B. Use this for flat scenes.

I guess you have a couple of options: increase time in Bath_A (which is a complete developer even on its own), or increase the strength of Bath_B (either by increasing concentration or substitution with something more alkaline)

Lots of scope for experimentation.

 

[Alex Benjamin]

Some thoughtful comments from an experienced user of Thornton's Two Bath here:

Effects of increasing Sodium Metaborate in BTTB

In general may I know what effect it will incur on the contrast when I increase the Sodium Metaborate say from 12g to 15g. My plan is to have slightly higher action Bath B(close to 20g, for winter) and cut back the development time for normal contrast to hight contrast scenes.

www.photrio.com

Thanks for this. I hadn't seen it. I did a title-only search with "Thornton" and did not think of searching using "BTTB"... Hard to understand some of the hostility toward BTTB in that thread, but David Allen's comments are very informative.

When I add Bath B in the tank I let it rest for one minute and do one very slow twist every minute.

I'm only developing 120 film, and doing it as Barry Thornton suggested, i.e., two or three hard taps after pouring B to dislodge air bubbles, and then letting it sit for three minutes before doing one inversion. I add another one at the 4-minute mark.