Dichromate bleach exhausting too fast

[narigas2006]

Hi All,

I have been developing some foma r100 i have and my bleach (K dichromate) keeps going bad very fast. The funny thing is that when it starts to exhaust, it bleaches the image but not the antihallation back. Is there anything I can do to 'ease' the bleach's job or 'revive it'? Also, should I replenish or should i just wait for it to stop working then make a whole new batch.

many thanks!

 

[Mike Wilde]

I don't know of your working practices, but I would sugget that after first developer, stop, then a couple of water rinses to remove any residual acid from the film. That might help. As to antihalation - I have mnot used this film , but some films may need a pre-bath before developer to get anti halation softened up. For foma, if it is not a hardened emulsion, a pre-bath may make the gelatin slogh off.

Usually a cromium bleach starts orange (like Tang, for the north americans here) and with exhaustion, turns to greenish. The valency state of the chrome thus signals its change. It is also less toxic in it's green state. So I reuse and filter, as necessary to remove any crud, between uses. I toss any unused film leaders in the almost exhausted chrome bleach to make it fully green before turning it in at the HHW site in my municipality.

 

[narigas2006]

afte the 1st developer, i generally wash in water but not much, that may be the reason. The color is still orange when it stops working. That is the part i don't understand... The funny thing is that the broth still bleaches ilford or orwo negs developed as reversal... Just some chemistry question here Mike, 1st thanks for the tip of throwing film leader. when it turns green, what happens? Also, the sodium sulphite clearing bath in the next step also turns green. so, do u think it is a good idea to mix the bleach and the clearing before disposal? i was just reading that foma uses the same antihallation as e6 films but i wasn't aware that e6 uses k dichrom. Many many thanks for the help!

 

[Ian Grant]

Are you using a plain Dichromate bleach or one with Sulphuric acid ? That makes a big difference to the way the bleach works, the ratio of acid to dichromate varies slightly in manufacturers published formulae but should be around equal gms of Dichromate to ml of conc Sulphuric acid, up to double the amount of acid.

Most of the silver halide bleaches change if the pH shifts.

Ian

 

[narigas2006]

i mix the chemicals myself and i was supposed to use 12g dichrom and 12ml sulfuric acid but i hate mixing it and i normally mistaken the quantities as i avoid taking to much time with the dichromate sitting in the weighing boat. So, one should keep the pH constant? Also, can I replenish old bleach? many thanks!

 

[Ian Grant]

Mix the bleach in two parts as 12% Solution and keep those on the shelf, they keep well that way. Then make up the bleach just before use. The pH is probably less important tha having sufficient Sulphuric acid to convert the processed part of the image to soluble Silver sulphates.

If you were processing commercially replenishing the bleach might be an option but it's far better to use fresh bleach ech time.

Ian

 

[narigas2006]

Thanks heaps Ian!

so, u think that if the solution is still orange and i cannot bleach the backing of the foma film, should i try to add a little more sulphuric acid? Thanks!