Polymer plate production problem


I am fairly new to polymer plate production, and am having a problem that I’m hoping forum members can help me with. I make hot foil dies, using polymer plates that can tolerate temperatures up to 180 degrees C. And the production method is identical to that of letterpress.

I am using the darkroom method to produce my plates. That is, I print out my image on to an acetate OHP sheet with an inkjet printer. I then transfer this image on to photographic film and then develop it with Developer and Fixative.

My problem is that the clear parts of the negative have a mottled appearance, which is then reproduced onto the plate. The consequence of this, is that my final image takes on a frosted appearance rather than a silky smooth one.

Is the problem down to my exposure times, or perhaps a problem with the film?. I initially expose the film for 12 seconds in a 8x15w plate maker under vacuum, before I develop it. After this, I place the film onto the polymer and put them under UV and vacuum, in the usual way.

For some jobs the frosted appearance of the image would look quite attractive, but I wouldn’t want it for every job.

Can anyone help with this issue?

Best wishes

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I not sure if this is the issue but it sounds like the opaque parts of the acetate from the inkjet are not dark enough to prevent light from reaching the film during exposure. I would try using a shorter exposure time when transferring the image to the film, to try and clean up the clear areas of the film, and I would make sure that your film is not fogged (already exposed to some light) and that your developer and fixer are fresh. Whatever is on the film is going to be on the plate.
Alternatively you could try looking to see if you can make the acetate print darker in the printer driver software or using a fresh ink cartridge. Best of luck!

Hello Stephen,

Bruce definitely has identified one possible cause. However there is another one as well. Let’s go through what happens when you expose silver based graphic arts film, which is what I assume you are using. The film has an emulsion layer, which is composed of particles of silver halide (a silver salt) in a layer of gelatinous material. When you expose the silver film with the inkjet film, light goes through the clear areas of the inkjet film, causing an invisible change in the emulsion layer of the silver film (which is called a latent image). Then, when you put the silver film in developer, this causes the grains of silver halide which have been exposed to light, to turn into silver metal, which is black. (There is no change in the unexposed grains of silver halide). So at this point the exposed areas of the film are black and the unexposed areas are sort of an opaque grayish color (which is the unexposed grains of silver halide in the emulsion layer). Then you put the film in fixer. The fixer dissolves away the unexposed silver halide and gelatin, turning the opaque grayish areas into clear areas. The end result is that the exposed areas of the film are black and the unexposed areas are clear. (I assume you are also washing the film well at the end, to get the residual processing chemicals out of it).

So what I’m saying is, the fixer step might not be washing out all of the grains of unexposed silver, leaving the mottled layer you speak of. The solution to this would be to leave the film in the fixer longer, until you can hold it up and not see any mottle but just clear areas. (You would have to do this under safelight of course).

Just out of curiosity, do you have to use a dim red safelight to avoid exposing your film, or a brighter yellow light. There used to be two different kinds of film.

Hi Stephen, What kind of film are you using? I have set up some older press cameras and shoot the artwork with them some call them field cameras,
I use a litho film and develop with paper developers.
I tried to use regular film and the development was always off. Not sure if it is to due with the fact that litho film is generally made for shooting artwork and the regular films are continuous tone. Do you know any local older photographers that maybe familiar with what you are using, with regular film no safe lights and with the litho you can use paper safe lights red.

OHP film? surely can’t get enough density with this…use coated dryfilms like grafolac or try digital transfer film( grafolac which I expose in the platemaker to the polymer)….going back to my days of gallery camera and wet film with lith film and developers, I think milky look is not enough fix and wash also-got to check are using the correct chemicals, and temperature also is a factor, red safelight for lithfilm..


Thank you for all your replies so far. I’m based in the UK, and I think that my terminology may be a little different from what is usually used in the USA. So apologies for any misunderstandings.

To be clear I print my image on an ordinary non photographic acetate and then place the acetate on top of my film in the UV unit for 12 seconds. I then place the film in developer, which causes the image to appear.

I think that Bruce may have a point about the UV light penetrating the black areas, I will use a shorter exposure time tomorrow and see if this helps. When making my images in Coreldraw, I use 100% black and I’m using the print menu in Coreldraw to print my images, but I’m not sure if my printer is printing as dense as it can. I use pdf files.

Geoffrey, I place my negative in the fixer for about 30 seconds. I don’t use any red or yellow lights. I just wait until dusk, then close the blinds in the bathroom. The black areas of the negatives come out perfectly black and I can’t see any light through them, it’s just the areas that are supposed to be clear that I’m having problems with.

As for the type of film I’m using, I’m not sure, to be honest. Like most people who hot foil in the UK, I get my film from a company called Polydiam. All I can say is that it comes in A4 sheets, is blue on one side and purple on the other. I’ve been placing my acetate positive on the purple side.

I’m not really disappointed with my results. I’ve only printed a few and I’ve been able to print from all except one of my attempts, and non of the plates have cracked. Apart from the frosting effect of the final plate, my only problem is knowing when to stop the washing process.

If I haven’t explained the method I’m using properly, I’ve been following the advice given in Chris Vasper’s blog, from the Quill Press here in the UK.


Best wishes

i checked out the quill press link-they say use water as hot as possible when washing out the polymer plate by hand—plates I have use have specific temperature and times for washout in a platemaker, so I would double check that with the spec of the plates you use.Also I rinse quickly with cold water after the machine has finished with the hot water.Quill also said dab with a (presumably?paper)kitchen towel to quickly dry the plate , polymer is still soft at this stage needs extra care, use hairdryer on back of the plate too, again plates usually have a spec for temperature and time of drying in platemaking machines.- could try a leather for car wash drying for first adsorption of water after plate is developed?…..but never made a plate for hotfoiling though………..Cheers


I just thought that I would post an update to my original question about the poor quality prints from my photopolymer plates.

After comments from forum members, I played with the print menu’s in Coreldraw, and I was able to get a much deeper black when printing out my positives on to an acetate sheet. I then reduced my initial exposure of the negative film from 12 to 7 seconds. Lastly, I soaked my negative in fixer for 60 seconds instead of the original 30 seconds, then I rinsed with plenty of water.

After these adjustments were made, the areas, which were supposed to be clear were indeed totally transparent, and the previous mottled effect had disappeared. As I followed all the suggestions that were mentioned by forum members, I’m not really sure which one was the key. What I can say, is that my latest prints are by far the best quality I’ve managed so far.

Thank you for all your helpful suggestions.


Stephen, thanks for getting back to us. It is always nice to find out how everything turned out. Glad your problem is solved.