In Piss Somewhat Warme...

Call me conservative, but there just has to be a better way to clean your nice shirts... although I do see the merit in that, regardless of the medieval event, both piss and beer are always readily available. Go to the right party, and ask nicely enough, and you could probably even get both in one go :-)

"A good way to washe a shirt, and saue the Gold or silke thereon, from stayning. First take a new shirt and lay the coller and ruffs or silke in piss somewhat warme for half an hour. Then take it out and then wash it in hot scalding liquor, or seeth it, and it shall never stain silk. If ye have no piss, you may take grounds of strong beer or ale, and let the silk lie in it the night before you wash it. And this has been often proved very reliable. But always you must take care that you don’t hang your clothes in the hot sun after they are washed, but lay another cloth thereon between the sun and it, or else the sun will change both Gold, Silver and Silk. Therefore it is better to hang them in some place of shade after their washing, if you can. Also, to add too much soap to your water is a good way to stain both gold and silk. A verie good way is, first to melt your sope in the licour, and then let it coole, and so to wash your clothes therin."

Source:
“A Profitable Booke,declaring diuers approoued Remedies, to take out spots and staines in Silkes, Veluets, Linnen and Woollen Clothes: With diuers Colours how to die Veluets and Silkes, Linnenn and Woollen, Fustian and Thread: Also to dresse Leather, and to colour Felles. How to guild, graue, sowder, and Vernish. And to harden and make soft Yron and Steele. Verie necessarie for all men, specially for those which haue or shall haue any doing therein: with a perfect Table hereunto, to finde all things readie, not the like reuealed in English heretofore. Taken out of Dutch, and Englished by L. M. Imprinted at London by Thomas Purfoot, dwelling within the Rents, in S. Nicholas Shambles. 1605. Transcription by Drea Leed This book is transcribed from a copy currently at the National Art Library in London, England. Although this is the 1605 edition, the original edition was printed in 1586. http://www.elizabethancostume.net/dyes/profitable.html