Last updated: October 2026
Quick answer: On a positive-working plate, the areas exposed to light or laser are removed in development and the unexposed coating prints. On a negative-working plate, the exposed areas harden and become the image. The working mode must match your film or platesetter; it is not a quality grade. We supply positive PS plates only, not negative PS plates.
Key takeaways
- Positive or negative describes how the coating reacts to light, not how good the plate is.
- Film workflows must match: positive PS plates need film positives; negative PS plates need film negatives.
- We manufacture positive PS plates and do not supply negative PS plates.
- On CTP the RIP handles polarity, but the plate still has a working mode: single- and double-layer thermal plates are positive; violet photopolymer and processless thermal plates are negative-working.
- Run length depends on the grade, baking and ink, not on the working mode alone.
Suppliers use positive and negative without explaining, and buyers are left guessing which plate to order. The words describe one thing: what happens to the coating where light hits it. Getting it wrong is expensive, because the plate came out reversed or blank and the job has to be remade. This article explains both working modes, lists which common plate types are positive or negative, and shows what to do if your workflow depends on a plate we do not supply. For a full map of plate families, see our article on the main types of CTP plates.
Positive vs negative plates: decision table
| Criterion | Positive-working plate | Negative-working plate |
|---|---|---|
| What light does | Makes exposed coating soluble | Hardens or anchors exposed coating |
| What prints | Unexposed areas | Exposed areas |
| Film needed (conventional) | Film positive | Film negative |
| Common examples | Positive PS, single- and double-layer thermal CTP, CTcP | Negative PS, violet photopolymer, processless thermal |
| Exposure fault shows as | Under-exposure leaves residual coating (toning) | Under-exposure gives weak or missing image areas |
| What we supply | Positive PS, thermal, CTcP | Violet photopolymer, processless thermal; no negative PS |
What is a positive-working plate?
On a positive-working plate, the coating becomes more soluble where it is exposed. The developer dissolves the exposed areas, and the unexposed coating stays as the ink-receiving image. In a film workflow you therefore expose through a film positive: the black areas on film protect the coating, and those areas print.
Our positive PS plate works this way and is exposed through film on a conventional exposure frame. Most thermal CTP plates are also positive: on our single-layer and double-layer thermal CTP plates, the 830 nm laser makes the exposed coating soluble in the developer. Our CTcP plates, imaged with UV light, are positive-working as well.
What is a negative-working plate?
On a negative-working plate, light or laser energy hardens, cross-links or anchors the coating. The developer, or the press itself, removes the unexposed areas, and the exposed areas print. In a film workflow you expose through a film negative.
Negative PS plates exist in the market, but we do not supply them. Among CTP plates, our violet photopolymer plates are negative-working: the violet laser starts polymerisation, preheat completes it on grades that need it, and the developer removes the unexposed areas. Our processless thermal plates are also negative-working: exposed areas become ink-receptive and the unexposed coating is cleared on press.
Which plate types are positive and which are negative?
| Plate type | Working mode | Imaging | Supplied by us? |
|---|---|---|---|
| PS plate (positive) | Positive | Film positive, UV exposure frame | Yes, made in our factory |
| PS plate (negative) | Negative | Film negative, UV exposure frame | No |
| Single-layer thermal | Positive | 830 nm thermal platesetter | Yes |
| Double-layer thermal | Positive | 830 nm thermal platesetter | Yes |
| Processless thermal | Negative | 830 nm thermal platesetter | Yes |
| CTcP (single-layer) | Positive | UV platesetter | Yes; no double-layer CTcP |
| Violet photopolymer | Negative | Violet platesetter | Yes |
Flexo plates follow the same idea: photopolymer flexographic plates are negative-working, because UV light hardens the relief through a film negative or a LAMS mask.
When to choose positive plates
- You run a film workflow with film positives on an exposure frame. A stable supply of positive PS plates is exactly what you need.
- You image on a thermal platesetter and want developer-processed plates, single-layer for general work or double-layer for UV inks and the longest baked runs.
- You run a UV platesetter and need CTcP plates for conventional-ink work.
When negative-working plates make sense
- You own a violet platesetter: violet photopolymer plates are the only plate family it images.
- You want to remove developer from the plate room: processless thermal plates are negative-working and develop on press. They can run UV inks after a trial.
- Your film workflow is built on film negatives. Here we have to be plain: we do not supply negative PS plates, so see the switching options below.
A common objection is that negative plates always last longer. That is not a rule. Run length depends on the grade, on baking and on the ink, and the grade TDS states it under its test conditions.
Can you switch or run both?
On CTP, polarity of the image is set in the RIP, so “positive or negative does not matter on CTP” is partly true for the file. The plate’s working mode still has to match the platesetter and the processing line. On film, polarity matters directly. If you tell us “we only have negative film”, the options are:
- Output film positives from your imagesetter or bureau, and use our positive PS plates on your existing exposure frame.
- Contact-copy existing negative film to positive film for repeat jobs.
- Move to CTP: a UV platesetter with CTcP plates keeps conventional-type plate chemistry and removes film entirely.
Changing film type is some work, but it is usually less than changing the press room. Plants that run both positive and negative plates should keep separate developers and processing settings for each grade.
Cost and workflow factors
| Factor | Positive plates | Negative-working plates |
|---|---|---|
| Film | Film positives (PS) | Film negatives (PS) or none on CTP |
| Processing | Developer, rinse, gum | Preheat and prewash (violet) or none (processless) |
| Plate room light | PS and CTcP: yellow safelight; thermal: room light within TDS limits | Violet: yellow safelight; processless: room light within TDS limits |
| Baking | Thermal and CTcP grades bakeable | Per grade TDS; processless plates are not baked |
| Price | Confirmed in the quotation | Confirmed in the quotation |
To choose a grade by press, ink and run length, use our plate selection guide. If you are moving from film to CTP, our CTP vs PS plate comparison covers the workflow change.
FAQ
What is the difference between positive and negative printing plates?
On a positive-working plate, exposed coating is removed in development and the unexposed areas print. On a negative-working plate, exposed coating hardens and becomes the printing image. The mode must match your film or platesetter.
Is a PS plate positive or negative?
PS plates exist in both versions. We manufacture positive PS plates, exposed through film positives, and we do not supply negative PS plates.
Are thermal CTP plates positive or negative working?
Our single-layer and double-layer thermal CTP plates are positive-working: the 830 nm laser makes the exposed coating soluble in the developer. Our processless thermal plates are negative-working.
Are processless plates positive or negative?
Our processless thermal plates are negative-working. The laser anchors the exposed coating as the image, and the unexposed coating is removed on press by fountain solution and ink.
Can I use a positive plate with negative film?
No. A positive plate exposed through negative film gives a reversed image. Output film positives instead, contact-copy your negatives to positives, or move to a CTcP or thermal CTP workflow without film.
Which is better, positive or negative plates?
Neither is better in itself. Choose the working mode your film or platesetter requires, then choose the grade by run length, ink and baking needs as stated in the grade TDS.
Not sure which working mode your workflow needs? Request a quote — tell us whether you run film or CTP, your platesetter type, plate size, gauge and inks. Or request trial plates / contact us.
Disclaimer: values on this page are typical and for reference only; final specifications, MOQ, price and lead time are subject to the grade TDS and the quotation.
