I have enlarged 6x6 negatives to 5x7 or 8x10 for cyanotypes and albumen prints. I've read that diluted print developer is often used, but I ended up mixing my own LC-1, which was formulated specifically for making enlarged negatives from Lith film. A documented advantage of LC-1 is a more linear density curve compared to diluted print developer.
I also used a step wedge to help see what was happening when making the interpositive as well as the final negative.
Here is a link to some pages from - Christopher James' "The Book of Alternative Photographic Processes" that discuss enlarged negatives and LC-1.
Originally Posted by Jim Noel
Jim --- WOW!
I've just skimmed it and I think it is exactly what I wanted.
Thank you very much. I just need the negative worthy of enlarging. If/when I have a question I will bring it to you. But as I read, you seem to anticipate and address issues before they become issues.
I've been making enlarged negatives all afternoon. I got some ortho litho film from Freestyle (cheaper than lith film in the UK unfortunately otherwise I'd buy it here) which you just use like you would paper under the enlarger. Develop by inspection in trays in ilford multigrade 1+9 dilution which takes about 40-50seconds. It's not that hard, I wish people would stop poopooing it and just shove themselves off to the d-route of doing it. From what I can tell, lith film can be more economical than ohp film too.
I didn't reply to this sooner because the OP seemed to suggest they wanted 8x10 enlarged to 16x20 which is a bit beyond most people's enlargers... but if they mean enlarging to 8x10 size, that's not hard.
I was using 4x5 fomapan100(panchromatic film) before I got the lith film and that's a little more fiddly, working in complete darkness but it does give nice results. I still had to use multigrade paper developer to get a nice high contrast result out of it, though (5 minutes dev time, in case anyone is wanting to repeat my workflow). So give it a try if you have a darkroom, you can get really huge lith film from Freestyle, and if it's not big enough they do 100-400ft rolls in various widths up to 40inches wide if I remember correctly...
I agree that developing by inspection is the way to go and the duping process is not technically hard. But getting the right contrast through the internegative to the positive (= the duped neg) is simply a bit laborious. So far I've only gotten it to work with negs for which the tone scale wasn't particularly subtle. Anyway, yeah, if you can get it to work for your neg, then great.
To get the interpositive - over expose and underdevelop so the positive falls in the mid Zones about III-VII. You should be able to see full detail in both highlights and shadows.
With a properly exposed and developed positive, the negative can be manipulated to any degree desired.
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If this process is done correctly, how does the final contact print of the larger negative compare to an enlargement (print) of the original negative ?
Originally Posted by Jim Noel
Is the goal here to make the two prints look different or the same ?
Does the contact print in this exercise lend itself to benefiting from the usual benefits of contact printing ?
Usually the purpose of making an enlarged negative is to make a print by a process that can only be done by contact printing, like pt/pd, albumen, cyanotype, gum bichromate, ziatype, vandyke brown, kallitype, etc.
Sorry, I wasn't clear enough in my question, I was referring to contacting printing onto AZO paper. Would the process of enlarging the neg result in a print of inferior quality  when printed onto AZO (compared to printing the smaller neg onto standard B&W paper)
Originally Posted by David A. Goldfarb
 Ignoring the recent thread about any 3D effects of AZO, perhaps such a subjective question about "quality" could be answered either subjectively from a personal preference or objectively on the grounds of tonality, accutance and grain.
Possibly the easiest and frustration free way to do this is to use duplicating film(negative/negative). The selection now is very limited. One seller on the auction site (mrphoto1) sells this film (up to 24" x 30"). If you find one of his items, the information on the page lists the various films and uses. Making a positive intermediate and a large negative can be a good learning experience. Keep accurate notes and eliminate as many variables as you can. Preflashing your film to .03 to .05 above base fog will help greatly. If you wish to minimize grain, when you make the enlargement, defocus the image. If carefully done; sometimes it is hardly noticable on the final print. I have never tried lith film as I had the equipment and materials to make any size negatives or duplicates.
There will always be a difference between a print made from the original and from a larger copy negative. A high quality copy will require a second look to tell. It is like COC.
I had a client who had me make 4 x 5 dupes from 8 x 10 negatives for non critical work because prints were a lot cheaper than contacts. One person could make and process over 500 8 x 10's per hour against 150 contacts per hour.
Why are there no speaker jacks on a stereo camera?
Thanks Richard. So done properly and using the same paper(if that were possible), it should not be overwhelmingly difficult to make the two prints look "the same".
Originally Posted by richard ide
(print 1 being an enlargement from 35mm neg to 8x10", print 2 being a contact print from the copied 8x10 neg)