Removable holder which fits between lensboard and lamphouse of an enlarger.Holds negative flat and in a fixed position. Can be glassed or glassless. Glass prevents negatives popping or buckling from heat of the lamp but introduces more surfaces for dust to settle on.
Orange or red light used in a darkroom.Gives out light of a wavelength to which photographics paper is relatively insensitive. Safelights are not actually safe. Leave paper exposed to a " safe " light close enough or for long enough and the paper will fog.
A few drops added at the end of washing reduce surface tension of water preventing droplets forming on surface during drying. As drops dry they leave a roughly circular " drying mark" of residue from the water.