which developer for zero fog?

[chris77]

hello apug, hello pe.

i am developing large paper sheets (coated with rollei/maco vc emulsion)

test strips show slight fog.

i used my standard paper dev. replenished LPD.
is it by any chance possible that developer could be the culprit? if not i am gonna recheck safelight.

i have also rollei rpn dev (hydroquinone) and dektol at hand.
any preference? or maybe less dilution shorter dev time? what is best??

tx for input and ideas
chris

 

[tezzasmall]

Hi Chris,

it's a process of ticking off various things to find the culprit that's causing the fogging, as it could be a number of things.

First off I would try and develop and fix a piece of the coated paper with out any light of any sort hitting it ie in total darkness, to check that you are getting a base white. This would confirm that the emulsion and developer are okay.

After this, as you asked straight away if it could be the safelight, I would check this by putting coins, one at a time on a small strip and exposing at various times up to just after the length of time you think would be the maximum you would have the paper out of the box.

These short test should help you find out the reason of the slight fog.

Terry S

 

[chris77]

Hi Chris,

it's a process of ticking off various things to find the culprit that's causing the fogging, as it could be a number of things.

First off I would try and develop and fix a piece of the coated paper with out any light of any sort hitting it ie in total darkness, to check that you are getting a base white. This would confirm that the emulsion and developer are okay.

After this, as you asked straight away if it could be the safelight, I would check this by putting coins, one at a time on a small strip and exposing at various times up to just after the length of time you think would be the maximum you would have the paper out of the box.

These short test should help you find out the reason of the slight fog.

Terry S

hello terry.
thank you for replying.

apart from all your good input (of which i am well aware) i am hoping to get a better understanding of chemistry in practical terms.
i know that the presence of certain chemicals induces fog.
so i am trying to find out which developer would be best in order to develop a thickly coated piece of paper and if dilution, temp, etc. also play a role...

best regards
chris

 

[Lachlan Young]

I'd suspect the safelights before anything else - the Fomabrom Variant emulsions (I recall RBM is made by Foma) can be pretty susceptible to safelight fogging - they really need red (Kodak 1A or better) safelights. How are you drying the paper & how long does it take? I've seen the fixed grade Foma liquid emulsion fog in as little as 10 minutes of exposure to a nominally 'safe' safelight - and it's much less green sensitive than the multigrade emulsion.

Until you solve this part, fiddling about with the relatively minor details of chemistry is fairly irrelevant.

 

[chris77]

I'd suspect the safelights before anything else - the Fomabrom Variant emulsions (I recall RBM is made by Foma) can be pretty susceptible to safelight fogging - they really need red (Kodak 1A or better) safelights. How are you drying the paper & how long does it take? I've seen the fixed grade Foma liquid emulsion fog in as little as 10 minutes of exposure to a nominally 'safe' safelight - and it's much less green sensitive than the multigrade emulsion.

Until you solve this part, fiddling about with the relatively minor details of chemistry is fairly irrelevant.

tx for your reply. i am just testing the safelight. looking good.
i am never drying coated stuff under safelight,always in the dark.
by the way, i cannot seem to find vc foma emulsion anywhere. where did you find out about black magic vc being foma?

 

[Photo Engineer]

A very thick coating on paper can also lead to fog.

PE

 

[Lachlan Young]

tx for your reply. i am just testing the safelight. looking good.
i am never drying coated stuff under safelight,always in the dark.
by the way, i cannot seem to find vc foma emulsion anywhere. where did you find out about black magic vc being foma?

No, there's no Foma VC liquid emulsion, but I recall that the specs of the RBM fixed grade were remarkably close to those of some of Foma's & sufficiently different from (for example) SE1 to make me suspect they may well share a lot of technology. Maco tend to be quite secretive as to who makes what in their range.

 

[chris77]

A very thick coating on paper can also lead to fog.

PE

hello pe.
tx for chiming in. why is that? actually fog seems more present when the coatings are thick. does it have to do with the way i coat? should i not let each layer dry?
and can i do something to reduce the fog on thickly coated paper??
thanks for your input!
chris

 

[chris77]

No, there's no Foma VC liquid emulsion, but I recall that the specs of the RBM fixed grade were remarkably close to those of some of Foma's & sufficiently different from (for example) SE1 to make me suspect they may well share a lot of technology. Maco tend to be quite secretive as to who makes what in their range.

true, but they are well known for making their own emulsion. at least they used to be...

 

[Photo Engineer]

hello pe.
tx for chiming in. why is that? actually fog seems more present when the coatings are thick. does it have to do with the way i coat? should i not let each layer dry?
and can i do something to reduce the fog on thickly coated paper??
thanks for your input!
chris

Film and paper, on average, require different amounts of silver halide to be coated in order to achieve proper imaging. This is due to the laws of physics. With film, the light goes through the image only one time, but in paper the light bounces back and forth multiple times giving higher fog, higher contrast and a limited Dmax. No matter what you do on paper, the average Dmax is about 2.0.

These multiple internal reflections may be the cause of your fog. Average film silver levels are often more than 2x that of paper, but of course that depends on the paper itself and the emulsion.

PE

 

[chris77]

Film and paper, on average, require different amounts of silver halide to be coated in order to achieve proper imaging. This is due to the laws of physics. With film, the light goes through the image only one time, but in paper the light bounces back and forth multiple times giving higher fog, higher contrast and a limited Dmax. No matter what you do on paper, the average Dmax is about 2.0.

These multiple internal reflections may be the cause of your fog. Average film silver levels are often more than 2x that of paper, but of course that depends on the paper itself and the emulsion.

PE

so in case of a rather thick coating on a thin paper, would it help to expose onto the paper in such way that the light doesnt bounce back? by going vertical and hanging a very absorbing black matte background behind the paper?

 

[Ian Grant]

Put your safe lights on a dimmer switch and turn it down as much as you can, Those of us who have been on Ilford factory tours will tell you just how low the levels are in the paper confectioning area at Mobberly.

Also make sure you have the right safe light filters they should be Ilford 902/Kodak OC which are light brown and far better for VC emulsions.

Ian

 

[chris77]

Put your safe lights on a dimmer switch and turn it down as much as you can, Those of us who have been on Ilford factory tours will tell you just how low the levels are in the paper confectioning area at Mobberly.

Also make sure you have the right safe light filters they should be Ilford 902/Kodak OC which are light brown and far better for VC emulsions.

Ian

thanks ian.
i do have 660nm led with rubylith on top to reduce brightness. still, when coating paper i need to see what i am doing, at least the first layer (wrinkles, bubbles, etc.).
if my safelight as is tested 100% safe for 5 minutes with fomabrom variant paper, should i be ok for the same time with the vc emulsion or is the chlorbrom really that much more sensitive?

 

[Ian Grant]

thanks ian.
i do have 660nm led with rubylith on top to reduce brightness. still, when coating paper i need to see what i am doing, at least the first layer (wrinkles, bubbles, etc.).
if my safelight as is tested 100% safe for 5 minutes with fomabrom variant paper, should i be ok for the same time with the vc emulsion or is the chlorbrom really that much more sensitive?

I'd prefer to use the correct OC/902 safelight these are the best for VC papers, you can have issues with Red unless specially made. You must be coating and handling the aper far longer than a normal pre-coated paper. Remember a normal safelight will fog paper if it's exposed to it for too long.

Ian

 

[chris77]

I'd prefer to use the correct OC/902 safelight these are the best for VC papers, you can have issues with Red unless specially made. You must be coating and handling the aper far longer than a normal pre-coated paper. Remember a normal safelight will fog paper if it's exposed to it for too long.

Ian

will restrainer help with this kind of fog?

 

[Ian Grant]

will restrainer help with this kind of fog?

Not really without affecting the lighter tones. It's better to try and cut safelight exposure to a minimum that's time and intensity. There's also something else that can happen with over exposure to Red safelights due to the Herschel effect, that can lower the contrast meaning you need to give longer exposures to get good blacks also affecting the highlights. I've seen this first hand and it eas why Paterson/Photoax brought out a specific VC safelight filter (similar to OC/902) it only happens in extreme circumstances, very small darkrooms or safelight too near the emulsion.

Ian

 

[chris77]

Not really without affecting the lighter tones. It's better to try and cut safelight exposure to a minimum that's time and intensity. There's also something else that can happen with over exposure to Red safelights due to the Herschel effect, that can lower the contrast meaning you need to give longer exposures to get good blacks also affecting the highlights. I've seen this first hand and it eas why Paterson/Photoax brought out a specific VC safelight filter (similar to OC/902) it only happens in extreme circumstances, very small darkrooms or safelight too near the emulsion.

Ian

thanks for making this clear.
i guess for the monent will have to practice with even less light as i still got 10 days in the darkroom before me and no possibility to buy different safelight.
got a darkroom out of nowhere, with the big advantage to work with a window open in new moon nights.
cheers and tx evrybody.
chris

 

[Photo Engineer]

so in case of a rather thick coating on a thin paper, would it help to expose onto the paper in such way that the light doesnt bounce back? by going vertical and hanging a very absorbing black matte background behind the paper?

If this is your problem, it cannot be fixed by most any means. Just coat thinner.

And, if you are working with a full moon, don't let the light into your darkroom!

PE

 

[chris77]

If this is your problem, it cannot be fixed by most any means. Just coat thinner.

And, if you are working with a full moon, don't let the light into your darkroom!

PE

now i am using approximately 125ml of emulsion for 1 m2.
before it might have been 150. so i am slowly cutting back as i want the highest density possible without fog.

.. and if its a red moon? would it be safe?

 

[Photo Engineer]

That is about the right amount of solution, but it also depends on how much silver is present per ml., and it also depends on the activity of the emulsion.

A red moon or any moonlight is unsafe. It contains some of the reflected UV from the sun.

PE

 

[chris77]

That is about the right amount of solution, but it also depends on how much silver is present per ml., and it also depends on the activity of the emulsion.

A red moon or any moonlight is unsafe. It contains some of the reflected UV from the sun.

PE

its the rollei black magic vc emulsion. i cannot say more about the content. do you have more info on it?

 

[Photo Engineer]

No. Contact the manufacturer.