> PMT stands for Photo Mechanical Transfer.
> They are shot two ways on a graphic copy (process camera).
> One ways is called a line shot. If you had a page of copy (words) or an
> illiustration with no value graduation in the tones then you could
> reproduce it as a line shot(no dots). A process camera will enlarge or
> reduce the final image from the original.
> The second is a halftone pmt. this is where you have a photograph or
> illiustration and it need to have halftone dots put in the copy so that it
> can be reproduced on a printing press. You lay a halftone screen over the
> pmt negative material and make the two nessecary exposures (1) main
> exposure is the actuatal copy of the original and then (2) the flash
> exposure which creates the white dots on the shadows. (look at the dots in
> the newspaper photo. the highlightsare blackdots on white and the shadow
> dots are white dots in the ink.
> Now run the neg. with the reciever paper through the processoer and
> "tada" you got a halftone pmt. Simple hugh? the pmt is usually waxed to the
> layout sheet and then shot onto line (lith) film to be prepared for making
> a printing plate. I used to do all of this for a living is why I can
> regurgatate this mess. the problem is in the halftone the dot is usually
> soft and you loose some when the pmt goes to film. Solution: Forget the pmt
> process and shoot the haltone directly onto line film. This saves two
> genarations of degrading of the image and countless amounts of time and
> materials.
> I am sure that I have you completly confused now. (not my
> intentions of course) I suggest that you find some books on the OFFset
> litho process or get a local offset printer to show you what and how all
> this works. It is all truly wonderful to see and do.
Yes, I am a bit confused. I guess I don't quit see why the pmt step is
necessary. I also don't know how the transfer process works. I guess as
you mentioned before this works in a similar fashion to the polaroid
process, namely development of the pmt material transfers the image to the
receiver sheet? I did recently pick up an old book on offset printing.
I'll have to see if it says anything about this.
> As far a
> conventiontial or non photo methods I have never seen where this tipe of
> processor would be of use.
Me either, I'm just curious. I do think I may be able to make use of the
contact print system.
> Let me confuse the issue a bit further! Is this
> gizmo two rollers one on top of the other and the trough is on the bottom
> so that a liquid could be added to the trough and touch the lower roller
> only?
I didn't get time to check, but I think that this might be the case.
> If so then you may have a plate coater. One adds a light sensitive diazo
> solution to the tray and the lower roller caries it up to the second
> roller. You run a plate throuth this thing and it coats the plate. let it
> dry and your ready to burn a plate. how wide is it. ours were about 36"
> across where the pmt machine was 12 to 18"
These dimensions sound about right. Perhaps this might work well as a
mechanical coating machine for something like a cyanotype?
- Wayde
(allen@boulder.nist.gov)