Wednesday, July 10, 2013

Not-Even-Trying-To-Be-Period Verdigris

Verdigris has been used throughout the medieval period as a green pigment. It has a fairly fine particle size and usually has a teal-like blue-green colour.

A number of recipes can be found within the medieval art treatises and they all seem to be variations of the following; suspend plates of copper over vinegar in a sealable jar for a number of days and keep the vinegar warm either by keeping it in a warm place or burying it in the dung/compost heap.

For an assignment I needed some verdigris, and I needed it quickly. Perfect timing for a quick, initial experiment before looking at this pigment more in-depth. There has been, and will be, more reading involved which no doubt will spawn another post at a later time.

Scrap copper pipe.
Day One (June 1, 2013): All I have on hand are very non-period tools and materials since this is a slightly spur-of-the-moment experiment which was born of a burst water pipe. When we opened up the wall to fix the leak I was really happy to find copper pipe, it's been sat waiting for me ever since.

My first step was to cut the pipe into more manageable pieces and discard the welded joints, for this I used a standard pipe-cutter available from any hardware store. I wasn't too concerned with the lengths being even so they range in size from about two to four inches.

Materials used.
For my "sealed pot" I used what was on hand, in this case a plastic tupperware bowl and and a zip-lock bag. To suspend the copper pipe I made holes at the top of the plastic bowl with a 1/4" diameter screw and then used wooden skewers fed through the holes and pipe. Into the bowl I poured about half an inch of Heinz Distilled White Vinegar (5% acidity).

Some translations call for the sealed pot to be buried in dung, but since I believe this is more to do with available temperature I'll be leaving my "pot" in a hot sunny location.

Day Two (June 2, 2013): Surprisingly, I already have an obvious patina of acetate forming on the copper pipe that was set up yesterday. I honestly wasn't expecting to see much of a result for at least a few days, if not weeks. That's not quite 24hrs and I already have some verdigris pigment forming.

This actually leads me to wonder just how much of a role temperature plays in this reaction? Would the acetate form just as quickly during the cold winter months?

 It looks "damp", which is most likely due to the amount of condensation visible in the ziplock bag but it definitely has the bluish-green colour typical of verdigris. I expect that when I harvest the pigment, the colour will dry a little lighter.

Copper acetate forming on the pipe.
Day Four (June 4, 2013): One drawback I'm discovering about doing this in a plastic ziplock bag is that it's creating a lot of condensation which drips onto the copper. (Is vinegar condensation, vinegar or water?). I'm pretty sure that this wouldn't happen in a sealed ceramic or metal pot, or maybe it does and that's why the period texts tell you to bury it in dung. It would certainly keep a more even temperature which I think would reduce or even eliminate the condensation.

Day Twenty Two (June 22, 2013): I got bored with watching it, not to mention I need to use it on something I'm working on.

It's a beautiful if not slightly windy day, so I set up my work area outside on the deck. To prevent the wind from blowing the pigment around I placed one of the stoneware dishes made for me by Bruni into a large plastic ziplock bag, this was to be my pigment catch-plate. I carefully opened the bag containing the vinegar and copper and proceeded to remove the first of the tubes with the help of tweezers, transferring it to the catch-plate. Wearing a fine-particle mask and latex gloves I then scratched the green pigment off the tube with a small metal palette knife, allowing it to fall onto the catch-plate. These steps were repeated for all five tubes. Once all the pigment had been scraped I transferred it into a small glass jar. This is known as "basic" verdigris.

Not-Even-Trying-To-Be-Period Verdigris being scraped from the copper piping.
Materials for the next batch.
Since I want this little experiment to continue, and to be honest I would like more verdigris since it's such a common medieval pigment, I've created a fresh container of vinegar and copper. My container this time is an old ceramic countertop compost pail I've had sitting around for the longest time, it's the closest I can get to a period "sealed container" without specifically buying something (I'll be checking out pottery wares at Pennsic). I've used the same Heinz Distilled White Vinegar (5% acidity), contained in a glass cup at the bottom of the pail which I've secured with wax to prevent slipping. I've used the same copper piping, albeit more of it which I've just randomly dumped in the pail, as opposed to hanging. I've used wax to secure the lid on the pail and to fill the vent holes, effectively sealing the container. My intent is just to leave it forgotten in the garden until the weather turns cool in the autumn.

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