Difficulty with Poly plates

I am trying to produce my own ploy plate, but am having difficulty.
The plates I have made do not have much of a “bank” on the side of the image it is very straight. Also I am losing the fine detail, periods and thin areas. I am exposing them on a vacuum frame with an Olec 1250 lamp and developing them by hand in the sink with a brush. My first thoughts are with the exposure, any ideas to get this to work? I do not have a Stoffer scale, I like the idea of not having to wait for the plate to be made and shipped to us.
Any help will be appreciated.
Thank you-

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Your light source is too much of a point source light to give you any width to the base of your lines. The exposure units designed for photopolymer exposure have flourescent bulbs which give more of a diffuse light pattern. Once the light enters the photopolymer, it spreads a bit and widens the shoulders as the light goes through the polymer.

One thing you might try to do is to put a matte or frosted film between the light source and the film/plate sandwich. I have used this technique in the past to make photopolymer plates on a conventional platemaker. You would have to increase the exposure times if you put something in there which absorbs some of the UV radiation. I have never tried anything but a thin film diffusuion sheeting, but perhaps a thin sheet of translucent acrylic might work. It should be available in a DIY store. Even waxed paper might work for a trial.

I agree with the previous post. I’ve always made them in- house and using my own lightsources. A stouffer gauge would be very useful, if not essential. I work with regular output film for press but also inkjet film for photogravure, A good diffuse lightsource that has a predictable UV output is what you need. Also distance from vacuum frame is important. Mine works at about 18inches height and is an old UV sunlamp.I use the film that covered the plate itself or I use a diffusion screen. A stouffer gauge would give you the opportunity to set up exposure tests and get that part right. Also when washing out using a soft brush and water at about 20-24 degrees. Take great care with this and don’t undercut. A nice slope is what you need and when drying watch out for dust and anything that might stick in the poly. I use a hairdryer for drying and lintless car wash cloths. Then post expose.

Are you doing a pre-exposure? 30 seconds usually does the trick on my platemaker. It gives my plates a nice shoulder and keeps the finer lines from going anywhere.

Boxcar sells Stoffer scales.

Thank you for the help- I tried a diffusion sheet and pre-exposure but still am not happy with the outcome. I think it must be my light source, I use film negs from an Accuset 1000 and a glass top vacuum frame. The exposure lamp is a Olec unit with the 1250 blue tip bulb, exposures are VERY long and results are not useable. I was thinking of making a light box with black lights to place over the glass for exposure.
Are these the best lamps for the exposure of this type of plates? The brush used to wash out, are the ones from Boxcar super soft? What is available locally that is close to try until I get one from Boxcar?
Thank you all

Pre-exposure (through the back) is used with film-backed plates, but not steel- or aluminum-backed plates. It would help if the original post said exactly what material is being exposed, otherwise there will be conflicting information.
You must get a Stouffer scale, and use it to find average exposure according to manufacturer’s specifications (different plates have different specs). Working blind is just throwing away time and material, and a Stouffer’s scale is cheaper than a single plate. Isolated dots and lines need longer exposure, as do fine serifs. A barrel-shaped dot or period is a clear indication of insufficient exposure.
I made photopolymer plates with a NuArc mercury vapor unit for many years, and know it can be done with extra care and effort, compared to a UV-tube unit made specifically for photopolymer. (And the UV-tube units really do work much better.)

Before I had a washout brush from Gene Becker, I used all kinds of brishes: stencil brushes, shoe brushes, painting pads, fabric-painting brushes.
Small brushes work for small plates, but larger plates need larger brushes. Ideally you want to cover the entire surface of the plate, otherwise you will be spending too long in the bath, and the plate may deteriorate before you have finished.


i just have to wonder how much this has cost you so far, in terms of actual cost as well as lost labor, with unsatisfactory results, compared to how much it would have cost you just having Boxcar or some other supplier make printable plates for you?

Really, I would like to know.