I've found a big improvement with that vacuum hot press, a trick is spraying some distilled water in the back before press, and after press I leave the prints to get cold between mat board sheets. No wave remains in the edges which is the most important, I guess.
Also I find that surface enhances when using silicone paper under emulsion. I may try again the method your point, but I'm impressed by the Drytac.
What I was getting at is that while it definitely flattens the paper very well, it doesn't do it as well as two bristol boards in a traditional dry mount press - which in its turn isn't as perfect as the drum-skin flat finish of a print dried taped under tension. The differences are, in the bigger picture, pretty small, but they are there & you have to pick & choose the compromises you are prepared to live with. More of a headache is the willingness of the silicone film to pick up all sorts of marks & microscopic debris & deboss them into the face of the print - cutting a new piece of film for every print gets old (and expensive) fast, but if you want a perfect finish, it's often necessary.
I use the permanent bond, neutral pH tissue - mainly because the heat de-bondable stuff doesn't have the best reputation for staying stuck & if a conservator really needs to de-bond the print, it can be done with solvents. If extreme archival permanence is necessary, I don't dry mount, I much prefer to use properly archival, fully reversible methods like float mounting etc.
The Durst 138 has an accessory they call LAPAL (not the LAPLA lens board ), it's a bare ground glass that's inserted in the filter drawer. With that you obtain a mid point between diffusion and condenser: callier effect disappears and still we have a powerful and efficient illumination, so you have best of diffusion and best of condenser. Degree of diffusuion can be adjusted with a more or less frosted glass. Then the bulb has a convenient XYZ position adjustment, compensating fall-off or generating it for aesthetics, it can even compensate off-axis fall-off produced when the view camera had shift/rise !!! This is a great advantage...
You should take a closer look at the 138's optical path - the LAPAL is intended to diffuse a projector bulb (
e.g. something like this Philips 375E) to deliver about the same coverage as the pear shaped monstrosities do. With the right opal glass & suitable heat extraction, you could probably run a much greater variety of bulbs than you might otherwise think.
For what you are intending however, placing a sheet of diffusion between the condensers will get you rather closer to what you propose.
Essentially the system is a semi-focused beam using a diffused opal bulb & clear condensers - if I were to design an LED system to allow you to continue to use the condensers, I'd make a diffused flat panel that matches the aperture hole between lamp box & mirror box - more importantly it eliminates the compromise Durst had to adopt in the late 1940's/ early 1950's to get even illumination. You could probably fabricate something that could drop in to the same slot as the filter holder. If I were going to dedicate the head to mural work, I'd seriously consider getting 200w of LED into the head.
I only stop until the lens sweet point, if light level is too high then I adjust the RGB LED power, which also allows easy split grade and it also works as a variable contrast head.
Most current enlarging lenses (depending on max aperture) hit optimal performance at f4.7-8 - going below that in a sharpness critical environment (like mural printing) becomes unpleasantly obvious rather quickly. Rodagon-G's are great for 135 & 120 & aren't necessary for larger formats unless you are going to truly extreme scales - do you need to go bigger than 40x50" or 48x60" - or are you writing about hypotheticals?
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