Rod coating results in faint lines

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David Marsh

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I'm rod coating salt prints (I have seen this happen with kallitypes too though) and when I coat the silver it leaves a faint outline wherever the solution is spread initially. I have tried all sorts of methods of coating, humidities when coating, etc and cant seem to knock them out completely. I've attached a picture to show what I mean, you may need to enlarge it since it is fairly faint. The solution is just silver nitrate in distilled water. I've also tried adding a drop or two of wetting agent and it's been hard for me to tell if it makes much a difference or not.
 

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nmp

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Welcome to Photrio!

OK...I see now. I had trouble pin-pointing where it was. These are the darker spots on the right edge running down perpendicularly right?

These are happening because as you pour or drop your liquid, it immediately starts getting absorbed in the paper and by the time you put rod on the paper and begin coating, those areas already have additional sensitizer than the rest of the paper. The primary cause of this obviously is a highly absorbent paper so the choice of the paper is the first line of defense. For example, when I was using Arches Aquarelle water color paper, it was quite annoyingly dominant. Recently I started using COT 320 paper (smooth side) and no sign of it, using the classic (2% salt, 2% silver nitrate, 6% citirc acid with no sizing) recipe.

Adding a wetting agent would probably have the opposite effect, I am afraid, as the propensity for absorption into the paper will be even greater. You can alleviate the problem somewhat by reducing the time between pouring and starting the stroke of the rod. Perhaps put the rod on the paper first, then the liquid and start the coating right away (I have a habit of doing the pouring and then looking for the rod.) I would also think, adding a sizing agent should help if you are not already doing so - either on the paper as a pre-treatment or within the salt solution. But now you are changing the process characteristics. Or perhaps you can put an opaque material over the area in question in exposure and develop it out - if you can afford the real estate.


:Niranjan.
 
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David Marsh

David Marsh

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Welcome to Photrio!

OK...I see now. I had trouble pin-pointing where it was. These are the darker spots on the right edge running down perpendicularly right?

These are happening because as you pour or drop your liquid, it immediately starts getting absorbed in the paper and by the time you put rod on the paper and begin coating, those areas already have additional sensitizer than the rest of the paper. The primary cause of this obviously is a highly absorbent paper so the choice of the paper is the first line of defense. For example, when I was using Arches Aquarelle water color paper, it was quite annoyingly dominant. Recently I started using COT 320 paper (smooth side) and no sign of it, using the classic (2% salt, 2% silver nitrate, 6% citirc acid with no sizing) recipe.

Adding a wetting agent would probably have the opposite effect, I am afraid, as the propensity for absorption into the paper will be even greater. You can alleviate the problem somewhat by reducing the time between pouring and starting the stroke of the rod. Perhaps put the rod on the paper first, then the liquid and start the coating right away (I have a habit of doing the pouring and then looking for the rod.) I would also think, adding a sizing agent should help if you are not already doing so - either on the paper as a pre-treatment or within the salt solution. But now you are changing the process characteristics. Or perhaps you can put an opaque material over the area in question in exposure and develop it out - if you can afford the real estate.


:Niranjan.

Thanks for the response! I'm not as concerned about the darker spots but if you look very closely there are very thin light lines that ring wherever the solution is first pooled. Almost like a water spot ring. If I do the coating right I can keep them limited to the outer borders of the coating area but sometimes they sneak in where I initially get the coverage going. I do have some cot 320 so perhaps I will do a test print with and without a size. I am using a pretty strong size, and also humidifying the paper each coat which I determined somewhere along the way helped minimize these, although it was a while ago so I should probably re-confirm that.
 

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nmp

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Darn...that's where I looked first and I thought that can't be it - have never seen those before so I presumed they were scanning artifact or something. You did say outline though.

So this looks like the opposite of the absorption - here whatever is happening is making those areas deficient of sensitizer or so it would seem. I don't think I can think of a theory behind this...not getting silver and citric mixed completely? Don't know.

:Niranjan.
 
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David Marsh

David Marsh

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I'm actually not using any citric acid, so whatever is creating that mark must be something it's interacting with in the paper I think. The salt / size is the only thing I can think of, it's possible that it's unavoidable, I've tried a handful of sizes and seen these on all of them, but I haven't tried a coating with no sizing agent yet. Something about the ring of surface tension around where the silver is puddled... I've also seen it when brush coating, in the spot where I initially pour the silver nitrate on the paper before I immediately start brushing.
 

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Is your rod wide enough to cover the area in one pass?
 
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Is your rod wide enough to cover the area in one pass?

yes, although I will still see these marks on the outer edges of the coated area. My process usually involves coating inside the image area leaving a "live edge" border, so I have to start the pour somewhere inside the image area (ideally). Also sometimes like in the print I posted in the first post the coating breaks up just going in one direction so I have to do a pass or two in different directions to achieve full coverage.
 

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Vaughn

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I have never done that (going in different directions with the rod). Starting in 2000 or so, I have been using a rod for pt/pd prints 4x5 to 11x14. I have used the 'live-edge' idea, also, but usually just for a rare image that calls for it...I usually do not compose in-camera for it. But it does save a little money not printing the full 11x14 negative!

I give the rod a little wriggle after loading it with solution along most its width with a syringe. This helps spread the solution along the rod and seems to reduce the coating from breaking up.

If there is a slight ridge of excess solution at the end of my last pass with the rod, I use a Q-tip to soak it up. Otherwise one ends up with a ridge of dry solution on top of the paper. This ridge increases the density of dry solution along it that can block some UV. This leaves a light line beneath it once the print is developed and that exposed and developed platinum on top of the paper floats off into one's tray. The platinum (and other similarly coated processes) need to be held by the fibers of the paper, not just sitting on top.

For a long while, I made two or three passes with the rod to define the coating area, than finish with a brush to get a even coat. I have gone back to just the rod. What works best depends on a combo of humidity, amount of solution used, the paper, patience, the process, and the phase of the moon, I swear!
 
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David Marsh

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I have never done that (going in different directions with the rod). Starting in 2000 or so, I have been using a rod for pt/pd prints 4x5 to 11x14. I have used the 'live-edge' idea, also, but usually just for a rare image that calls for it...I usually do not compose in-camera for it. But it does save a little money not printing the full 11x14 negative!

I give the rod a little wriggle after loading it with solution along most its width with a syringe. This helps spread the solution along the rod and seems to reduce the coating from breaking up.

If there is a slight ridge of excess solution at the end of my last pass with the rod, I use a Q-tip to soak it up. Otherwise one ends up with a ridge of dry solution on top of the paper. This ridge increases the density of dry solution along it that can block some UV. This leaves a light line beneath it once the print is developed and that exposed and developed platinum on top of the paper floats off into one's tray. The platinum (and other similarly coated processes) need to be held by the fibers of the paper, not just sitting on top.

For a long while, I made two or three passes with the rod to define the coating area, than finish with a brush to get a even coat. I have gone back to just the rod. What works best depends on a combo of humidity, amount of solution used, the paper, patience, the process, and the phase of the moon, I swear!

Thats a great idea to use a q-tip, it doesn't leave a mark on the coating where it touches?
 

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It can if one appiles pressure with a dry Q-tip. I go lightly to just soak up the excess solution without touching the paper. But since it is on the edge I do not worry too much about it. Inside the image area would be a different story -- that is where I would use a brush to spead the ridge out before it dies...and before it unevenly soaks some of the solution into the paper along the ridge.
 

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My process usually involves coating inside the image area leaving a "live edge" border, so I have to start the pour somewhere inside the image area (ideally).

Frankly, I don't see how you could ever prevent some sort of marks, density variation etc. by taking this approach. In fact, I think you got about as far as humanly possible the way you're doing it.
For further improvement, I would suggest looking at paper sizing mostly to manage the absorbance and adherence of the silver chloride to the surface. Trying different papers will help as well.

Very nice print BTW! Is that a salt print? It looks like a different kind of sensitizer; Van Dyke Brown perhaps?

Btw, contrary to @Vaughn, I do always do passes in opposite directions with the rod. Using a small excess of sensitizer helps to create a puddle that can be pushed back in the opposite direction after the first pass, filling in any gaps that might have occurred. This is the balancing act, as well: you either run a little lean on the sensitizer/silver nitrate and you run the risk of coating gaps. Or you use a little excess, but then you have a puddle to clean up and the point where that puddle collects after your last pass generally shows up in one way or another on the print. I tend to keep the start and end positions of the rod outside the image area to deal with this. Not an option if you want to coat everything within the image area, of course...

I'm actually not using any citric acid

And you get no staining? If you don't, how can you tell if you don't print with masked borders? Just curious; I never managed to make a salt print that did not fog without adding some citric acid to the sensitizer. It doesn't necessarily show unless I mask the borders. It's the only way I know of to ensure I've got the process right.
 

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...
Btw, contrary to @Vaughn, I do always do passes in opposite directions with the rod.
Sorry I was not clear. I do go back and forth -- I just make no passes in the direction 90 degrees in the original direction...
 
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David Marsh

David Marsh

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Frankly, I don't see how you could ever prevent some sort of marks, density variation etc. by taking this approach. In fact, I think you got about as far as humanly possible the way you're doing it.
For further improvement, I would suggest looking at paper sizing mostly to manage the absorbance and adherence of the silver chloride to the surface. Trying different papers will help as well.

Very nice print BTW! Is that a salt print? It looks like a different kind of sensitizer; Van Dyke Brown perhaps?

Btw, contrary to @Vaughn, I do always do passes in opposite directions with the rod. Using a small excess of sensitizer helps to create a puddle that can be pushed back in the opposite direction after the first pass, filling in any gaps that might have occurred. This is the balancing act, as well: you either run a little lean on the sensitizer/silver nitrate and you run the risk of coating gaps. Or you use a little excess, but then you have a puddle to clean up and the point where that puddle collects after your last pass generally shows up in one way or another on the print. I tend to keep the start and end positions of the rod outside the image area to deal with this. Not an option if you want to coat everything within the image area, of course...



And you get no staining? If you don't, how can you tell if you don't print with masked borders? Just curious; I never managed to make a salt print that did not fog without adding some citric acid to the sensitizer. It doesn't necessarily show unless I mask the borders. It's the only way I know of to ensure I've got the process right.

Yes, this is a salt print - it's much more brown and red than my normal process because I was using a large amount of salt in the initial washes and probably a more expired gold toner.

I have gotten to finding the sweet spot in the amount of silver solution (for me I have found it is 40 drops for my image area of about 10"x13") where I have enough to get uniform coverage and it takes me probably 20 passes and 5 minutes of going back and forth until there is very little excess remaining. I could probably start dialing that back even more but I'm afraid of losing density if I do, a lot of the literature says the more silver you can put on the paper the better.

I have not had an issue with fogging, but I alway print and process immediately after coating so it's only sitting out for about 30 minutes to dry.
 

koraks

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20 passes and 5 minutes

You must be using very resilient paper. If I would try this with my paper, I would seriously compromise the surface, with fibers becoming dislodged etc. And it would also mean much of the silver actually ends up embedded deeply into the paper where the fixer can't reach it very well. I have serious concerns about how well your prints can be fixed without bleaching them. Btw, drying time has very little to do with this.

a lot of the literature says the more silver you can put on the paper the better.

I would disagree with that. You only need enough silver to reach desired dmax. Any excess will just (hopefully) wash and fix out. Your 40 drops sounds like you're erring slightly on the high side, although not ridiculously so; I need about 0.7ml of silver nitrate to coat a 5x6" area, after which I still need to dab up maybe 20-25% after a couple of passes with the coating rod.
 
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You must be using very resilient paper. If I would try this with my paper, I would seriously compromise the surface, with fibers becoming dislodged etc. And it would also mean much of the silver actually ends up embedded deeply into the paper where the fixer can't reach it very well. I have serious concerns about how well your prints can be fixed without bleaching them. Btw, drying time has very little to do with this.



I would disagree with that. You only need enough silver to reach desired dmax. Any excess will just (hopefully) wash and fix out. Your 40 drops sounds like you're erring slightly on the high side, although not ridiculously so; I need about 0.7ml of silver nitrate to coat a 5x6" area, after which I still need to dab up maybe 20-25% after a couple of passes with the coating rod.

I am using HPR, I had to do a lot of trial and error with paper humidity and sizing so that the paper will lie completely flat. If it does not lie completely flat and retain it's flexibility it will show where the rod has rubbed repeatedly on the surface. I also use very light pressure on the rod, basically no more than the weight of the rod itself.

I am fixing with neutral rapid fix in two baths of 5 minutes each, I have not observed any bleaching. Afterwards I hypoclear for 5 minutes and then wash for 1 hour with continuous agitation and water changes every 5 minutes.

Based on how much solution you are describing is left after a few coats I don't think we are using radically different amounts of solution, but I am basically continuing to push it until it's almost completely gone instead of trying to remove the excess. I also may have exaggerated as to the amount of passes it takes, I have never actually counted or timed it. I am also using a fairly strong size that I do a double coating of, so there is some barrier to the silver soaking in too far.
 

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I am using HPR, I had to do a lot of trial and error with paper humidity and sizing so that the paper will lie completely flat. If it does not lie completely flat and retain it's flexibility it will show where the rod has rubbed repeatedly on the surface. I also use very light pressure on the rod, basically no more than the weight of the rod itself.

I am fixing with neutral rapid fix in two baths of 5 minutes each, I have not observed any bleaching. Afterwards I hypoclear for 5 minutes and then wash for 1 hour with continuous agitation and water changes every 5 minutes.

Based on how much solution you are describing is left after a few coats I don't think we are using radically different amounts of solution, but I am basically continuing to push it until it's almost completely gone instead of trying to remove the excess. I also may have exaggerated as to the amount of passes it takes, I have never actually counted or timed it. I am also using a fairly strong size that I do a double coating of, so there is some barrier to the silver soaking in too far.

Have you done a study of how much density you are gaining for doing say 10 passes vs 20 passes, in your particular set of conditions? I have found that after a certain number, it does not change the density much as the limiting factor then is not the amount of silver but the self-masking effect or even bronzing, beyond which there is no gain in the Dmax.

:Niranjan.
 
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David Marsh

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Have you done a study of how much density you are gaining for doing say 10 passes vs 20 passes, in your particular set of conditions? I have found that after a certain number, it does not change the density much as the limiting factor then is not the amount of silver but the self-masking effect or even bronzing, beyond which there is no gain in the Dmax.

:Niranjan.

No, but I would not be surprised if you are correct that there is very little difference. I mainly started going down that road because I was so concerned (probably without much reason) that any blotting or other methods for removing the excess solution would leave a disturbance in the coating.
 

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I have not observed any bleaching

Insufficient fixing / retained silver won't show up as bleaching, but as fog. It tends to appear after a while and get worse over time. Basically the print deteriorates. It's something to look out for, especially because your process doesn't have a good indicator of this not happening. I'd recommend making a print where you mask the edges from time to time to verify your whites clear and keep clean after a few days. I learned this the hard way...
 
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I have been doing prints for about 8 months and have a stack of probably 100 of them, I did wrestle with keeping a paper white initially (which would usually show immediately or once fully dried) but after a lot of refinements to my processing I have not notice any issue with the whites keeping clear. I do have a few prints that got some fixer splashed on them which turned an ugly brown / yellow - is that the effect that would happen across the entire print? I am always comparing the white of the non coated paper edge to the highlights in the image to ensure they are a similar brightness / color. Is it safe to assume that if I don't notice any deterioration after a few months that it will probably never occur?
 

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Is it safe to assume that if I don't notice any deterioration after a few months that it will probably never occur?

I would say so. Well, actually, only time will tell, and the odds of an untoned salt print fading are pretty high, but I understand you do tone. There's so much that can go wrong with a salt print in the long term, but personally, if it doesn't change at all in a few months, I'd call it good enough. Then again, I don't sell them, so it's just my own requirements that count. yMMV and all that.
 

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No, but I would not be surprised if you are correct that there is very little difference. I mainly started going down that road because I was so concerned (probably without much reason) that any blotting or other methods for removing the excess solution would leave a disturbance in the coating.

You have a unique problem with the "live" border requirement that you have go back and forth until all silver is absorbed. I coat the whole paper so when my requisite number of (7 or 9) passes are done, I just let the remaining liquid to run off the paper from the trailing edge onto a tissue paper. More time spent during coating more is the warping of the paper - looks like humidification is one way to counter that, as you seem to be doing. What I do is coat the paper in the direction perpendicular to the fiber direction, so the warp is from front to back and not side to side (which would mess up the point of contact between the rod and the paper, putting more pressure in the center vs the sides.)


:Niranjan.
 

nmp

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I have been doing prints for about 8 months and have a stack of probably 100 of them, I did wrestle with keeping a paper white initially (which would usually show immediately or once fully dried) but after a lot of refinements to my processing I have not notice any issue with the whites keeping clear. I do have a few prints that got some fixer splashed on them which turned an ugly brown / yellow - is that the effect that would happen across the entire print? I am always comparing the white of the non coated paper edge to the highlights in the image to ensure they are a similar brightness / color. Is it safe to assume that if I don't notice any deterioration after a few months that it will probably never occur?

Put a piece of white area (coated but not exposed) in the Sun and you will know if you have fixed enough. I have been doing a study, both for adequate fixing and washing and the results are surprising. I will write it up and share here, hopefully soon.

:Niranjan.
 
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David Marsh

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Thanks for all the discussion, it has been very difficult to find others doing salt prints online. This is a print I just did yesterday, I kept the humidity very high and used no wetting agent in the silver coating. I think it might have reduced the coating lines I was talking about some, although it is such a fine degree that it is hard to know.
 

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