How to trim a print/tissue sandwich?

Assume I've already adhered mounting tissue to the print,
and that I want to trim to remove the print borders and
excess tissue. My understanding is that I should undercut
the mounting tissue by holding the trimming knife at an
angle. This means I can't use my Rota-Trim, which only
cuts vertically.

How do I ensure that the trimmed print ends up perfectly
rectangular? I have a nice cork-backed straightedge, it's
the alignment problem I'm pondering.

Thanks!

I use an Olfa rotary trimmer with a see-through plastic ruler with metal edge.

I don't consciously try to undercut the tissue - just hold the trimmer as close to vertical as I can. It may not be perfect, but it's close enough.

I leave a generous white border around the image and tack the drymount tissue leaving a slight overlap at the edge which I trim with a rotary trimmer taking about 1/8th of an inch of the white photo paper. Done this for 25 years and never had a problem.

So you're saying you simply pre-trim the tissue to size?

That will work if I want to leave a white border, but is
more difficult since I don't. I suppose I could always
measure, pre-cut, and tack the tissue to the print on
a light-box..

Steve Goldstein said:

Assume I've already adhered mounting tissue to the print,
and that I want to trim to remove the print borders and
excess tissue. My understanding is that I should undercut
the mounting tissue by holding the trimming knife at an
angle. This means I can't use my Rota-Trim, which only
cuts vertically.

How do I ensure that the trimmed print ends up perfectly
rectangular? I have a nice cork-backed straightedge, it's
the alignment problem I'm pondering.

Thanks!

Click to expand...

By all means use your Rota Trim - that is what it was designed for.

Unfortunately, the plastic transparent edge piece that runs along the cutting edge does not come from the factory aligned properly. It is "short" of the precise cutting edge where it should be and as a result, it is less than optimal.

The solution unfortunately is to acquire a replacement plastic edge piece one size up and cut and fit it precisely at the cutting edge. For my 24" Rotatrim I needed to purchase the 30" plastic edge piece but once I carefully installed the edge piece precisely at the cutting edge I was good to go and I can tell you that after this modification it is a surgical instrument.

One decision as to a square cut affords the ability to use this edge along the edge guide for the remaining cuts.

For my contact prints I have a negative edge reference point that makes it very easy to trim to square with only the smallest loss of image area.

Cheers!

after tacking the mounting tissue to the print, we just use a rotary trimmer and cut off the white edges, or as les suggested we leave a wider white border and just trim about 1/8 of inch all the way around.

never have had an issues

I use my Rotatrim, no problems...EC

I shine short standed shop light upward at the edge of the Rotatrim, which is sitting at the edge of the bench. This transluces the print so I can see exactly where the edge of the trimmer is, and so the cut is exact. Never bothered "undercutting" Flush cutting has always gotton the job done. YMMV

i used to just use a metal straight edge and a blade.
haven't done it in a long while though.
a rototrim or equiv, would do a better job than a shakey hand ...

What I have seen, especially with fiber-based paper, is that one needs to dry the print in the mount press before attaching the tissue and trimming the print. This is more important than undercutting it.

The reason is that the print has moisture in the paper -- even when air dried for many days. (Those who live in areas of low humidity may not have this happening...it is always greater than 50% humidity where I live.)

Moisture causes the paper to swell slightly and get bigger. It shrinks when it dries. Therefore if one does not pre-dry the print before trimming, it will dry while being mounted...and shrink slightly. The mount tissue does not shrink and what happens is that one has a little mount tissue showing around the edges of the now smaller print. Photopaper tends to shrink in one direction more than the other, so often one will see the tissue sticking out of only two sides.

RC paper probably sees less shrinking since any moisture in it is locked between plastic.

I tend to use a straight-edge and razor blade to trim the print as the print is smaller than the window...and sometimes I need to trim somewhere around a 1/16" off one end and nothing off the other end to square it precisely in the window. I can't do that on a rotary trimmer easily.

Vaughn

Thanks all for the comments. I did my first-ever mount yesterday, just a scrap print on some junker board I had, but with pre-drying the print and using the Rotatrim I had no adhesive bleed at all, which was my concern.

Great, Steve!

How did you pre-dry? I follow the press' recommendation -- closed for 30 seconds, then open and close the mount press three or four times (drives out the moisture, supposively.) Seems to work...I dry the matboard first, then lay the print face down on the hot matboard and dry both together. With our high humidity, and therefore the relatively high moisture content of the matbaord, I dry out the matboard to keep any moisture from building up between the tissue and the matboard.

I dry mount 16x20 prints onto 24x28 mountboard -- I tend to get a little anal about the process. I really hate messing one up!

Vaughn