- What’s the difference in quality between polymer and lead type?
- What’s the difference between photopolymer plates and magnesium plates?
- What are the differences between steel-backed and polyester-backed photopolymer plates?
- What do I need to know about washing photopolymer plates?
- With experience what sort of detail can I hold on a photopolymer plate? How fine of a line can I hold? What's the smallest type that will work?
- Is there a preferred LPI for halftones?
- On a platen or lever press, how do you attach the photopolymer plate into the chase?
- How many impressions can I get off a photopolymer plate?
- Most of my plate is printing fine, but one or two areas of the plate are printing heavy. Does this mean the world is ending?
- If I’m scanning in an image to make a polymer plate, what resolution should the scan be?

Q: What’s the difference in quality between polymer and lead type?     

A: Photopolymer provides a strong consistent printing surface that can give you the same high quality and crispness as freshly cast lead type. Photopolymer provides a more consistent printing surface than lead type. The quality of printing using photopolymer is as sharp and crisp as the best foundry type, but without any differences of height between letters. In addition, polymer never wears down: your photopolymer will stay crisp, no matter how many print runs you do.
If you want a heavy impression, you generally don’t have to worry about damaging your photopolymer. Unlike lead type, which can be permanently damaged from heavy impression, photopolymer could potentially crack but will not compress and distort. On the other hand, if you want to print with the lightest impression, polymer is suited for the job because of its level surface; you won’t have to compensate for uneven heights of any parts of the type set.
Other advantages include being able to design sophisticated graphics using graphics software such as Corel Draw, never running out of type characters, having a huge range of fonts in limitless sizes, borders and graphics and much more. With photopolymer, you can also integrate images, line drawings, and halftones into your text you can create halftones. When printing multiple colour work in polymer, you are able to separate the different colour elements in your graphics software, then make the different negatives, followed by polymer plates and then you are ready to print. Computer typesetting allows you to proof any layout in seconds without investment in type metal.
Another important benefit is that polymer plates can be filed easily so retrieving the plate is easy, while with metal type you would normally dismantle the chase so the whole job would have to be re-set.

Q: What’s the difference between photopolymer plates and magnesium plates?

A: Magnesium plates are much thicker and heavier than photopolymer. Because they’re often mounted at type high, they take up more storage space than thin polymer plates (which can be stored in a filing cabinet). Magnesium plates also require more maintenance if you want to keep them around. After letterpress printing, you’ll have to coat them with an oil or grease, such as Vaseline or vegetable oil, or else the plate will oxidize over time and render the plate unusable.
To keep costs down, many printers use magnesium plates with wooden bases. If you use too much oil on your plate, then the extra oil could sink into the wood and potentially warp the wood base. Using wood as a base also has its own weaknesses: the wood warps with changes in atmosphere conditions and requires a lot more make ready than polymer.
 Photopolymer does not need any coating to protect its surface for storage. If you store your plates in a self sealing / zip lock bag in a cool, dry place away from UV light, your plates will last years (the plate must not be exposed to humidity). We believe that for letterpress printing, photopolymer plates are easier to print and will, with professional platemaking, produce a higher quality printed piece in the end.
Magnesium plates are well suited to hot-foil stamping as they heat up more quickly and evenly and require a shorter dwell time while polymer hot foil plates needs higher working temperatures and slightly longer dwell time. However where polymer plates beat magnesium hands down is the time and the cost to make your own. You could be printing within 40 minutes of the artwork printing off your laser printer.

 Q: What are the differences between steel-backed and polyester-backed photopolymer plates?

A: Both types of plates have same printing surfaces made from photopolymer. Polyester-backed plates however are traditionally used in rotary letterpress and have many advantages for those who print on cylinder and platen presses. They’re easier to handle and have better registration systems than steel-backed plates (which in the past have commonly been used in flatbed letterpress printing).
Steel-backed plates are rigid and don’t bend well. This inflexibility causes plates to kink and warp so that their corners work up on the press. In addition, you must use metal shears to trim these plates, which leave the plates’ with sharp edges. To print on steel-backed plates, you need the rather imperfect magnetic base to hold the plates at type-high. Magnets effectively hold a plate from peeling but cannot always hold a plate from moving side to side. The cylinder or rollers of a press can move steel-backed plates out of register, causing plate creep.
In contrast, polyester-backed plates are very flexible and retain their flatness even after being bent. Even though the plate is flexible, polyester-backed plate will retain its thickness just as well as steel-backed plates, even during the hardest impression. The die mounting adhesive tape that holds the polyester-backed plates to the base will peel off easily off the base. However there will be no sideways movement and so the plate will never move out of register on the press (avoiding plate creep). It is much easier to cut the polyester-back plate as you only need a pair of scissors and you are not left with sharp edges.
Polyester-backed plates though yellowy gold in colour are also transparent. This makes registration simple when used with a grid marked base, because you’ll be able to see the grid through your plate for perfect registration.

Q: What do I need to know about washing photopolymer plates?

A: A good washout is essential to producing quality photopolymer plates. The hand held plate washing pad is small and if washing A4 size plates the washout times are frequently are over 10 minutes per plate (and that’s if you are moving the pad with constant motion).  The adhesive coating used to bond the polymer material to the polyester or steel plate starts to break down after seven minutes. This causes loss of detail because the plate literally comes apart in the water.  We therefore recommend you wash smaller sizes of plate at a time and if you are regularly washing A4 size plates than we suggest that you invest in the PLX – A4 platemaker. Like with most things you do, with experience you will be able to produce plates the holds the finest of detail (within the polymer plate’s scope and specification).

Q: With experience what sort of detail can I hold on a photopolymer plate? How fine of a line can I hold? What's the smallest type that will work?

A: With experienced you could, when processing a polymer plate, produce a line as thin as 0.1 point/.0015" thickness and 2 pt. type face. If you plan on processing the plates, the amount of detail you can hold depends on your equipment and your platemaking skill. With polymer plates, you're mostly limited by your printing process and not by the plate material itself.          

Q: Is there a preferred LPI for halftones?

A: We don't recommend a single halftone line screen because your necessary line screen will depend more on the paper and presswork than the actual polymer plate. Our plates can hold detail to 150 line screen, but such a high line screen would be very difficult to print. The finest line screen that we usually process is 133 lpi, although we would even question the use of 133 lpi, except on coated or hard papers. Certainly 100 lpi would work on most documents  but some printers prefer playing it safe and go for 85 or 65 lpi. That way you have fewer inking problems when you're printing. The dpi of the image should be one and a half times the size of the lpi: for a 133 lpi image, make the image in the greyscale colour mode with at least 200 dpi.

Q: On a platen or lever press, how do you attach the photopolymer plate into the chase?

A: First, you would mount the thin photopolymer plate onto a base.  Then you would lock the base, into the chase with quoins and furniture just like you would a handset type form.

Q: How many impressions can I get off a photopolymer plate?

A: If you take care of them, the plates will last for as many impressions as you need them for. Photopolymer plates, in commercial applications, lasts for millions of impressions - the polymer is incredibly hard and durable.

Q: Most of my plate is printing fine, but one or two areas of the plate are printing heavy. Does this mean the world is ending?     

A: The problem may be due to air bubbles. Check to see if there are air bubbles between the adhesive tape and the plate in the affected area. These should be visible without having to peel up the plate. If you notice a bubble, poke a hole in the plate through a non-printing area with a sharp knife to pop the bubble (polyester backed plates only). If this is impossible because the bubble is directly under a printing area, peel the plate part way off and pierce the bubble through the adhesive tape instead.
Most other causes of heavy inking areas are due to roller height and incorrectly fitted base or chase. There is a chance that your plate wasn't processed correctly, which can cause some areas to print darker.
The adhesive on my polyester-backed photopolymer plate has dirt or grime on it.
You'll only need to replace the adhesive if the dirt or grime is under a printing area. If that's the case, peel off the old adhesive tape and replace it with new adhesive tape.  Take great care when removing the adhesive tape, because the plate may, during this process, crease unnaturally and kink the polyester backing. If this happens, you need to make a new polymer plate. In most cases though, careful peeling will remove the adhesive tape without a problem. Try and keep the plate from flexing inordinately while you carefully pull the adhesive off the back of the polymer plate. Then replace the old adhesive tape with a new piece of adhesive tape and trim it to the size of the plate. Mount the polymer plate onto the black and into the chase. Now you're ready to print again!
Please tell me, very specifically, how to put new adhesive on an old plate.
This should be a pretty easy process! Make sure you're putting the side of the adhesive tape that is exposed (without a release liner) down on the plate. The side with the release liner attaches to the base. When you first mount the adhesive to the plate, start with one side of the plate and roll out the plate so that it makes as few bubbles as possible. If the bubbles appear, then work them out with your fingers or pierce them, through the adhesive, with a knife or awl. You should be able to get all the bubbles out at this point.
If bubbles form underneath the plate when you mount it to the base, first try working these out with your fingers to the edges of the plate. If that fails, you can puncture the bubbles by sticking a knife or awl through the plastic backing of the plate to release the trapped air.                    

Q: If I’m scanning in an image to make a polymer plate, what resolution should the scan be?

A: To produce clean line art, scan the image at least at 600dpi and preferably at 1200dpi or higher. Save your file in the Bitmap or Line art mode. You can use 300dpi scan if you require a halftone. Keep the image in a greyscale colour mode in your graphics application, and the line screen of for example, 133lpi. We recommend scanning the image in greyscale, make adjustments to the image curves and levels, and convert the mode via Mode>Bitmap...>50% Threshold.