Masking a 120 Negative for Contact Print

I am interested in making a few contact prints of 6x6 and 6x9 negatives using split-grade printing on multigrade paper. I am wondering if anyone who has done this can share their technique for masking the negative. I have a 4 bladed easel, and thought I might just mask it using that, but I just tested it and there is a small gap between the negative and paper due to the curvature of the film (maybe this is not that big a deal?). I'm also not sure that anything thin enough to use under glass sandwiched with the negative and paper would be opaque enough to leave a good white border. Any ideas?

Buy a sheet of rubylith and cut a mask out of it. It is used in graphic arts, shouldn't be too hard to find.

You definitely want glass on top to contact print. You want a decent amount of pressure to keep the negative pressed to the paper.

Thanks!

Near impossible to do. A friend that did a lot of medium format contact printing trimmed the prints close to the image border and dry-mounted them to a larger matboard; they looked very good. The way I do it, to get it perfectly centered with a nice border is projection printing at 1:1 with an enlarger; no headaches when you do it that way. With an 80mm lens you need 160mm of bellows draw. If you are using a 4x5 enlarger, that will not be a problem.

The way used to do it that I did not like, was to cut the negatives to individual frames. Then try to lay the individual negative on the glass of a contact printing frame and have it square and centered and not moving, then carefully lay the paper on top and seal up the back of the frame. Then when I turned it over, the negative should be perfectly centered on the paper ( but never was ).

You can use plain black construction paper. You can mask your neg by taping the paper cutout on top of your glass.

I recently created borders on contact prints using pin stripe tape from the auto parts store. I purchased black 1/4" pin stripe tape and taped it to the non-emulsion side of the negative. This was a 4x5 negative. it slightly cropped the negative because I kept the tape right at the edge of the negative, I'm using 4x6 post card paper to print to. This allowed me to align the negative with the paper easier. I use an old contact printer that has the built in bulb it looks like a small toaster oven. The lid has a foam backing that presses the negative and paper together so they make good contact even if there is a slight variation in thickness with the tape. No light got through the pin stripe tape and it made a nice white border. They sell the tape in a variety of sizes and it can be pealed off the back of the negative when you're done.

Thanks for the suggestions. I see some 3 mil rubylith (which I had never heard of before) in various sizes on ebay, and I think I am going to give that a try. Being translucent, I am hoping it might make it a little easier to line things up. I can see how it would be tricky--makes you appreciate the 4 blade easels! I do have a 105mm lens for my Beseler 23CII, so I should be able to make very small, if not 1:1 enlargements, and I also have various strengths of ND gels cut to size to make the exposure times reasonable for those small prints. I'm really interested to see how the contact prints differ from a 1:1 (or close to it) enlargement. I will report back!

Since image circle doubles at 1:1 you can use a shorter focal length lens.
Also, when focusing be careful as there are two focal points. The one you are familiar with is associated with the image getting bigger when the head is raised. The other focal point is associated with the image getting smaller than 1:1 as the head is raised.
https://www.photrio.com/forum/threads/cool-enlarger-trick.43223/