Today (3/26/16) I taught my period pigments class again and we played with some of the pigments I made in 2015. Re-reading this post today I realized that I have learned a lot since then and need to update you all with a new post. I promise this will happen soon after Easter, aka tomorrow.
In the meantime you can explore my page of references, here.
Collecting the blue iris blossoms as they bloomed, May 30th, 2015 for over a week, I ended up with several hundred flower heads in two gallon sized zip-lock bags. Taking the advice of Wendy Feldberg, I froze them for later use. Though there were not freezers in medieval Europe, this seemed like a reasonable compromise with modern obligations.
The chemicals and linen I ordered from Dharma Trading Co. arrived! I used the wrong alum in these recipes, aluminum sulfate. It should be 'rock alum' which is evidently potassium aluminum sulfate. In 2016 I used the correct alum with pretty much the same results. Blue clothlets when they were wet changing to green the more they dried and painting out green.
I washed all of the linen with modern washing machine soap (Free and Clear Tide) and a 1/4 cup of white vinegar.
Not sure of the weights of medieval linen I ordered a yard of each of the three weights available from Dharma Trading Co. 3.5oz, 5oz and 8oz for making clothlets.
In the Materials and Techniques of Medieval Painting by Daniel V. Thompson, iris green is described (171). Clothlets are mentioned but not well defined and the process is never described.
Courtesy of Clair Turner I learned that the Glossary of the British Library describes it in depth:
A piece of cloth impregnated with PIGMENT (generally a vegetable dye). A portion of such cloth, when soaked in a little BINDING MEDIUM, releases its colorant and produces an artist's pigment. Clothlets are called petiae in Latin and pezze or pezzette in Italian; bisetus folii refers to clothlets dyed with folium, or turnsole, extract. Clothlets were a convenient way of carrying or shipping vegetal pigments, and they were especially popular from the fourteenth century on, with the growth of the textile trade. Glazes of vegetal dyes were often used to enhance other colours in book ILLUMINATION, since they created a rich, glowing, and transparent effect.
Randy Asplund then clued me in to Mary Merrifield's Original Treatices and there I found my recipes.
I was excited to get started and in a hurry to get something accomplished so I did what all of my friends and family would tell you I do with all of the recipes I work with: combine techniques from several sources and hope for the best, modifying behavior for the next round based on results!
Also found references in the anonymous treatise De Arte Illuminandi (translated by Varney pgs 7, 15).