Difference between positive plates and negative plates?

[realmstar]

Most metal plates are made with negatives of course. But can anyone with experience who has used positive metal plates burnt with positive film tell me what the differences is? Obviously its easier to proof a positive then a negative so I assume everyone would do positive plates but they don't. What is the difference in quality? Or are they exactly the same?

 

[gordo]

Most metal plates are made with negatives of course. But can anyone with experience who has used positive metal plates burnt with positive film tell me what the differences is? Obviously its easier to proof a positive then a negative so I assume everyone would do positive plates but they don't. What is the difference in quality? Or are they exactly the same?

If you're using film to burn the plates the "quality" will be the same. The difference will be the dot gain/loss on the plate. If the film in both cases is linear then negative film will have slightly positive dot gain on plate and positive film will have slightly negative dot gain on plate. Very fine type and lines may also appear as slightly different weights because of the difference in plate gain.

 

[aqazi81]

Here in Pakistan we use positive plates only and as Gordo said you will experience a bit of dot loss if over exposed.

 

[Repro_Pro]

Some more points:
Economics: some Negative Working analogue plates were made double sided. You could actually get two sides "for the price of one" (approximately).
Processing: Positive Working plates could sometimes be processed in the the same processor (same chemistry as CTP plates) - NOT ALL developers, but quite a few.