Fugazi Dave said:
As for negative popping, I only ever ran into the problem with 4x5. Initially I took to taping the netagive down under tension so it didn't have any slack to pop with, but it was a pain and I ended up getting the 4x5 neg carrier with the AN glass in it. Some may claim dust issues with glass carriers, but I've only had minimal trouble to this end and the benefits mean I'll likely never go back to a glassless carrier for 4x5, especially for Polaroid 55 negs.
Dave,
I have never trusted glassless carriers for large-format negatives, and even panoramic format negatives on 120 rollfilm. The custom carrier I have constructed for my 4"X5" Wasp enlarger has its main body as a flat piece of material with the image area carefully cut out, and then a sheet of ConTact paper is stuck to the top, without stretching: it is better to pull off the wax backing paper first, leave the sticky ConTact paper to stablise, and then apply. Then, the ConTact paper is cut with a scarpel to leave an aperture, slightly larger than the the rectangular hole for the image area, which corresponds exactly to the physical size of the negative. It helps if you can make some paper templates first, of course.
At the far end of the carrier, about an inch of the ConTact paper is also removed, and a good-quality thin adhesive tape is used as a hinge for a sheet of glass which folds down to hold the negative down.Since the ConTact paper is thinner than the thickness of the negative, the glass sits comfortably on top of the negative, exerting even weight over its entire area.
When a negative gets warm, the emulsion shrinks a little, making the it bulges on the support side. This arrangement effectively banishes that, and the lacking of glass on the underside also means two fewer surfaces to collect dust in the image path.
I use standard glass from my local picture framer and have no problem with Newton's Rings. If I were to be really pedantic, the best way is to have coated glass, but then it is also effective to "coat" it yourself: mix up a weak solution of gum arabic (as used for gum printing) and put it in a little spray bottle. Lay the glass down on a stack of newspaper, and gently spray over it, letting the droplets to settle by gravity. When dry, you should be able to see a slight mottling over the surface, like the colours produced by a thin film of oil floating on water: home-made coated "anti-Newton" glass.