I think the one question I've been asked the most about weaving with singles, is how do you size the warp? I've only found a few written instructions. Amos Alden's Big Book of Handspinning has recipes for several different warp sizings and is fairly easy to come by since it's still in print. I've been told all sorts of different things and I'm sure there are some privately published and smaller books with this info in it as well.
Here is my method and recipe. It's easy, inexpensive, easy to wash out and it works. While I worked it out before I read the above book, it's pretty similar.
Double Strength Gelatin Wool Sizing
If you can find powdered gelatin in bulk, it is much more inexpensive than buying the little name brand packets. Each packet would hold 2.5 tsps (12 mls) and it gels 2 cups (500 mls) of water . In a measuring cup, put 1/2 cup (125 mls) of cold water. Take 2 packets or 5 tsps of gelatin and stir into the cold water. This is an important step. The gelatin must soften in cold water first or it won't dissolve properly later. After 5 or 10 minutes, put 2 cups of water in a pot and start to heat it. When it's hot, but not boiling, stir in the now goopy gelatin mixutre. Stir until dissolved and liquid. Turn off the heat and let it cool somewhat to just lukewarm. It shouldn't start to set. If it does, just heat it up a bit to soften again.
If I'm using the singles for a larger project, I'll mix up a double batch from the beginning. By using the cold soaking water as supplementary liquid, I've found I don't have to add anything to thin it out a bit later. I've always had to otherwise.
Take your skeins, set them to soak in the lukewarm gelatin mixture. Squeeze out as much of the excess liquid as you can, back into the pot and hang the skeins to dry. I've put in pre-wetted skeins and dry skeins. Dry skeins absorb more gelatin and maybe a bit more heavily sized but both work just fine. Depending on how much active twist there is in the yarn, I've both weighted the skeins and left them to hang naturally.
One the skeins are dry, wind them into cakes or balls for dressing the loom or whatever process you normally use at this point.
I'm working with the warp for the hood project. It sized up nicely and winding it into a warp was no issue at all. This is the Z twist yarn. Because my pattern is 19 threads - 10 Z twist and 9 S twist, I'm marking the ends grouped in the appropriate numbers. This way when slaying I can just thread all the Z twist ends first leaving spaces for the S twist ends later.
Problems? You bet... I can't count! Somehow I thought I had enough yarn and that 3 skeins of each would do it. This is the first cake of yarn; 1 skein. This is 60 threads of Z twist.... I need 310 for doing the twill. Even if the other skeins are longer, I won't have nearly enough. I redid my calculations today and sure enough, I'd plugged a wrong number into my little spread sheet program, which made a rather enormous difference. Yikes.. I won't have the warp wound for our deadline but I'm still hoping to have it off the loom to put on display at an SCA event in November.