Egg float test used in 15th century?

Looking into fabric cleaning recipes I quickly found myself digging through old dyeing manuals, including the Segreti per Colori, or "Secrets of Color", an early to mid 15th century manuscript in latinized Italian. The Latin text of the manuscript and its English translation forms a major part of Mary Merrifield's Original Treatises on the Arts of Painting, published in 1849. The section on dyeing fabric, coloring leather and making chamois is in Volume 2, Chapter VIII, and includes one recipe on making musk soap. 

From Mrs Merrifield: "THIS MS. is of the fifteenth century. It is a small volume in duodecimo, on cotton paper, and is preserved in the Library of the R. R. Canonici Regolari in the convent of S. Salvatore in Bologna. It is numbered 165. On the outside of the fly-leaf is written "D'acquisto di D. Gio. Giuseppe Trombelli," and on the other side of the same "Libro di P. Gio. Batta Nozzi, di carte 240." The precise date of the MS. is not mentioned, but there are allusions to circumstances which seem to fix the date to the first quarter, or at latest, to the middle of the fifteenth century."

The intriguing part of this manuscript is that the soap recipe clearly uses the egg float test as part of testing the strength of lye. If Mrs. Merrifield correctly dated the MS to the early to mid part of the 15th century, then this mention precedes the oldest dated recipe known, from the 1558 The secretes of the reuerende Maister Alexis of Piemount by Girolamo Ruscelli, by more than onehundred years...

It is my feeling that if the technique was known at that time, dyeing manuals like the Allerley Mackel and the T bouck va wondre (1513) should also have mentioned it, which they did not. This makes me think this soap recipe is a later addition to an older manuscript, even though it was not marked as such (newer handwriting was marked with a "B"). The technique itself does get mentioned matter of fact in 16th century latinized Italian manuscripts like the Isabella Cortese and the Notandissimi, and of course the original Italian printing of the Alexis, in a similar way as in this MS.

221. To make musk soap.—Take a vase of whatever size you like, made of good earth,  and let it be rather thick in order that the weight of the lime may not break it, and near the bottom of it there must be a hole, closed with a peg, and on the inside, in front of the hole, you must put a wooden platter, and upon the platter you must put a lump of tow, enough to cover the bottom of the jar, and upon the tow, in front of the hole, put a small piece of thin linen. Then mix two parts of ashes from the baths with one part of quicklime, and place the mass upon the piece of linen that is upon the tow in the vase, and spread it well all over it. Then take rain-water, according to the quantity of the ashes, and pour it into the vase at two or three times, because it boils up and absorbs the water, and there must be enough water to cover the ashes to the depth of two fingers'-breadth or less, and when it ceases to boil, let it stand for a whole night, and in the morning take out the peg and let out the ley; and when you have drawn off a bocale full of it, pour it back into the vase, and it will become rather thick; do this two or three times, and the last time let it rest a little, and then strain it; and if it comes away too fast, press the ashes down a little in the vase, because it must issue from the whole like a thread in order that the ley may run off clear. And when the ley has entirely run off so that the ashes remain dry, take half a jug of water, and pour it over the ashes in the vase, and when it is strained pour it back 3 or 4 times into the vase, and the last time draw off the ley clear. And if you wish to know whether the ley is properly made, put a fresh egg in it; if the egg goes to the bottom it is not good, and if the egg floats it is good. Then take 9 bocali of this ley, and one roll of deer's or cow's tallow, which makes lb. 2 oz. 9, and melt it well over the fire; and when it is well boiled pour it into this ley, and keep stirring it for the space of half an hour; then let it rest for a night or more, and if you wish to add musk or any other scent to it, reduce it to a fine powder, and add it to the tallow which is in the ley, mix it up well and let it settle. Then put the soap in the sun in order that it may refine itself better, and it will harden so that you may make it up into balls, and it is done.

221. A fare sapone moschato.—Habbi uno vaso de la capacita che tu voj facto di bona terra et sia ben grosso a cio la possanza de la calcina non lo rompa et apresso del fondo vole esser uno bugio el quale se convene serrare cum uno spinello e dal canto dentro nante el bugio se vole metarce uno tagliere et sopra al tagliere se vole metarce una faldella de capecio che copra el fondo del vaso et sopra el capecio nante al bugio mectice uno poco de peza rada poi tolli doi parte de cenera de bagno et una parte de calcina viva poi la incorpora cum la cenere poi la pone sopra a la peza che e sopra al capeccio in lo vaso et distendila bene per tutto poi tolli aqua pioviana secondo secondo che e la cenera et mectila in el vaso in doi o 3 fiate per che ella bolle et resciugase et vole esser tanta aqua che stia sopra ala cenera doi deta o manco et quando non bolle piu lassa stare cusi tucta una nocte et la matina cavala spinella et lassa colare el capitello et quando naj cavato uno bocale remitilo disopra al vaso et vira uno poco brutto et questo fa doi o tre volte et lultima volta lassa uno poco reposare poi lassa colare et se venisse troppo forte calca uno poco la cenera del vaso perche la spinella vole gietare a filo acio che lo capitello vengna netto e bello poi che lo capitello e tutto vinuto che la cenera sia senza aqua tollj meza brocha daqua et metila sopra ala cencra che c in lo vaso et colata che sera rcmectila 3 o 4 volte suso in lo vaso et lultima volta recoglie el capitello chiaro. Et se voj sapere quando lo capitello e facto fino se conoscc in questo modo tiene uno ovo frescho desopra sc lovo va al fondo non e fino et sc sta a galla e fino. De poi tolli 9 bocali de questo capitello et uno rotulo de sego de cervo o de vacha che sonno librc 2, 2 [oz. ?] novc e fallo bene strugiare al foco et bene bolito metarlo in questo capitello et sempre remenalo per spatio de meza hora poi lo lassa possare una nottc o piu et se tn ce volj metere musco o altre cose odirifare pulverizale bene subtili et metili sopra al sego che e in lo capitello et mistiealo bene de vantaggio poi lo pone a reposare poi lo pone al sole acio che se afina meglio et restringerasse per modo che lo porai a palotare e de facto. 

Bocale, bocal; a liquid measure used at Rome, answering to what is called a bottle with us, it holds rather above an English quart. One boccale is 4 quartucci. Terracotta or glass vase, for liquids employed throughout Corsica and northern and central Italy. With many, many variations, averaging about 1 liter for wine, and 2 liter for oil.

Measurement translation from Italian Weights and Measures from the Middle Ages to the Nineteenth Century, Volume 145 Ronald Edward Zupko, American Philosophical Society, 1981. Courtesy of Google.books preview.

Free download of Volume 2 at:

https://books.google.com/books?id=44RAAAAAYAAJ&dq=inauthor:%22Mary+Philadelphia+Merrifield%22&source=gbs_navlinks_s

Chapter VIII transcribed at:
http://www.elizabethancostume.net/dyes/segreti.htm