Well, I've already learned something. Thanks! And I'm not the one who asked.
So here's what I have to add, but it may well be more than anyone wants to take on; can get pretty complicated.
My method with cyanotype (and this contradicts akki14, but I'm considering how to incorporate her logic, which seems pretty important) is to use an entirely unsized (waterleaf) paper of the type used by fanatic intaglio printers. The BFK unsized is great, or Arches 88. This stuff is very much like blotter paper but stronger and holds up in the wash for a long time. And it must be washed for a long time. Maybe someone has a bit of insight that could shorten this for me; I'd be grateful.
I apply the cyanotype solution to the BACKSIDE of the paper. It soaks through, and spreads outward due to capillarity. This filters any weird stuff out. It also makes the paper rather soggy when it is wet, and it will bulge out.
Then the big problem is to dry it. For this, I built myself a negative pressure box using three 120v. muffin fans that suck the air out. The door where I put the papers in to dry, hanging on wires with clothespins, leaks. This is important. It must leak, or holes must be drilled in the bottom, or both. On the face of this box is a piece of glass (must be kept clean), and outside is an array of ruby infrared lamps such as they use to keep broiled chickens warm enough to keep them from spoiling. I turn everything on, in a darkened room (well, lit by insect bulbs and the ruby lamps) and allow time to dry thoroughly. VERY thoroughly. Damp does NOT WORK.
To expose the images I prefer a platemaker with a vacuum frame because the paper will still not be flat, and it will also be stiff. If you don't have a vacuum frame, and don't have a platemaker, you can make a vac frame using some 1x2's for an outer frame and internal baffles with masonite on the back, and pegboard on the top, and some pvc parts to make a way to attach it to your vacuum cleaner - which, if it's any good, really sucks. This will require a top sheet, and the clothes bags cut open to make a single layer sheet (buy them from the vending machines at the laundromat) work admirably for this.
In my younger foolish days I used sunlamp bulbs. No thanks! But you can use it with sunlight (be sure your extension cord is big enough) or blacklight tubes, or a mercury streetlamp. You will need to determine the exposure but I do it visually; when the greenish material surrounding the negative is a sort of a bronze color (I know it when I see it) it is done.
I have a tray that hooks to the faucet and has holes for draining at the other end. These things need to wash for a long time.. I suspect that alternating soak/wash, soak wash would work best, but since I just learned about this (being extremely old and a general curmudgeon) I've never tried it.
Then, when the water runs clear, and you are sure of it (better be sure of it; it will develop a brownish stain around the image if you aren't), hang it to dry. I use the same box, or just hang on the line if I'm in production.
Here are some examples: http://www.pbase.com/bullis/two_canyons
And another: http://www.apug.org/gallery/showphot...5&ppuser=26530
If you try this, I sure want to know what you discover. Sure glad I built the stuff for this long ago. Would I go through it now?