Yes, according to my experience citric acid is the best organic acid for cyanotypes. Depending on the paper base, it might stain or yellow the highlights somewhat, but it gives deeper blues than acetic acid which is often recommended - and easily available as vinegar. To some extend, of course, this remains a matter of taste, of how you would like your pictures to look.
Originally Posted by Davec101
Dave, you refer to Cyanotype II - is this New Cyanotype or just traditional cyanotype with citric? If it is New C., then I think you should, with hydrochloric or nitric acid for the first wash (see Mike Ware's website), get much deeper blues still, the border being very nearly black.
Bowzart, i.m.e. the image degradation during the wash is (of course) due to slightly alkaline, or hard water. Here acetic acid/vinegar comes handy: you may just add some to the dish every few minutes (depending on your water flow) in order to stabilize the image. The colour will be more cyan, though, which you might like to adjust with a short wash with plain water in the end, with a short dip in a week dichromate solution, or with a weak solution with a weak alkali (I use sodium sulfite) near the end - the latter has to be exercised carefully, it gives you purplish highlights (and clears them) which you might or might not find attractive (I do).