Hand developed Photopolymer?

So in my formal training we had a plate developer for photopolymer and the institution that I am at now does not have a plate developer or the money to get one in the future. I have been playing around with hand developing the plates. The exposure unit I am using is one for silkscreen but I didn’t know if anyone out there has gone down this road before and if they had any success or advice that I could use.

The other tough part is we are limited as well to films a bit I have been stacking laser transparencies (I know this is not the best thing by far). I was taught in a traditional darkroom with a copy camera and kodalith films. But we cant do anything like that here so I have been trying to give my printmaking students the photopolymer experience the best I can with what we have. Any Ideas?

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I am realizing that there are many threads on this so sorry for the question but if there are any specific threads or points advice can be given it would be much appreciated.



I looked at that along the way. I have a full exposure unit set up for silkscreen and for alternative photo processes but I am getting ok results but I think my problems probably come from films and hand washing more than anything. It seems as though I will expose a plate and I have to be careful in washing out after a couple of minutes I can start to loose detail. I tried longer exposure with no real difference in effect.
Any ideas?

Forgive my skepticism, but I also started exposing PP on a silkscreen set-up and I doubt you’re exposing long enough.

A photopolymer screen printing stencil is much thinner than a photopolymer plate and much softer. Are you familiar with step-wedge tests?

Screen printing photopolymer needs to be exposed to a solid step 7 on a 21 step test and letterpress plates need to hold a solid step 18. It’s a logarithmic scale, so for each step you need to move up, you raise your exposure 1.5 times if I remember correctly. That being said, you will normally need to expose PP on a silkscreen set-up 1.5^9 or about 40 times longer, which is usually not possible.

To hold fine detail, bulbs that peak at the proper UV spectrum will be required (350nm if I remember correctly?,) as well as very high quality negatives and exposure through kreene, not glass, which will diffuse light correctly and give the relief a shoulder.

Different makes of plate specify different steps on the Stoufffer scale; read the instructions for the plate you are using. Step 18 is definitely not standard to all plates; 16 is a correct starting point for Rigilon MS plates, with adjustments needed for specific image types. For example a thin isolated line needs longer exposure than the same width of line in crosshatching, and less exposure as a reverse. Fine serifs also need longer exposure to hold detail.
And absolutely, high resolution silver negatives are fundamental to getting typographic plates of any quality. Line art and coarse display typography can be done with less.

Parallel_imp is definitely correct in that you should always read plate specs. The step 18 is for plates sold by Boxcarpress.

Just to clarify I am using photopolymer plates for letterpress but using a silkscreen exposure unit for exposing the plate. The bulbs are 6 black light UVA bulbs (f30t8/ bl350)
The plates I have are Rigilon MS-152 plates so maybe the 16 point would be a start. Does anyone have any estimation for ballpark exposure. I have been getting decent results at short time of around 2 minutes but it is tedious washout to keep the detail.

Like parrallel_imp and I were saying, the only way to calculate exposure time is with a step-wedge test—it will give you instant feedback about the hardness of your plate. You can buy a 21 step test direct from Stouffer, Boxcar sells them as well. Burn a plate with it and using the instructions that accompany it you can calculate exposure time.

A friend of mine who has a 4 bulb blacklight unit set-up is still underexposing and shoots for 20 minutes.

The distance between bulb and plate is as importan as exact number of bulbs. In a commercial photopolymer unit it is only a couple inches, but I have seen other setups where it is feet away (over a big fliptop), and then much longer exposures were needed.
Three and a half minutes is a commion exposure on three units I have used, and a fourth required 7 minutes (old tubes). You don’t always need to washout everything down to the backing. If you are losing serifs or other detail you might reduce washout as well as increase exposure.

Thanks so much for all the help I will try and do a test plate and give an update.


PS I attached an image of something funny I don’t know if anyone has ever seen. I had a test plate that I left in the sun to post expose and it started to rain and I totally forgot about it and when i came back this is what the rain did to the plate.

image: rainplate.jpg


A Jet plate, right? :—)


Miraclon looks like that when in the bath too long. When the adhesive layer dampens and fails, and the photopolymer is no longer in contact with the yellow layer (an antihalation layer?), the photopolymer shows as white. The green Rigilon material goes blueish in the same conditions.

Well I used my epson for film printing and it works amazing now. On my test plate I got down to 5pt font that printed great. and can get deep relief. Thank you guys so much for your help. I also found a great wash out brush for $1.98 it is the brush for painting corners and trim work. It has a short nap and worked amazing.

Thanks again