You might have noticed I’m interested in medieval (and Tudor) stuff and chemistry, although the inspiration for this small project came from something that should be compulsory for re-enactors.
Namely, looking at period illustrations.
(Some periods are excused due to the lack of decent illustrations)

So, whilst perusing 15th century interiors in such pictures as this:

The Weyden Annunciation

Apprentice Writers

I noticed the presence and popularity of red cushions.
Sure, maybe that’s just because red is a nice bright colour for your painting. But then we know they also liked nice bright red clothing, so it is likely that they had nice bright interiors like the pictures show. In fact not just likely, but more like they did if they could afford it. For instance they’ve redecorated rooms in Dover castle and the Tower of London to roughly what they were like in the high medieval period, and there’s lots of bright colours there, including reds.

Anyway, back to the experiment. The internet is, as usual, full of slightly conflicting recipes, so I kind of averaged them out.
The very first thing was to wash the wool (A nice tightly woven worsted twill) and rinse it clean.
The next day I boiled it in alum solution, 129.7g of wool so 25.8g of alum.
(Don’t worry about the decimal point, that’s just me showing off my kitchen scales)

Boiled for an hour and 45 mins at around 85-90°C.
It was then left for 4 days to age. Only I did this bit in the week I was ill, so wasn’t able to complete it, so I left it to dry out, deliberately. It was then boiled again in the same water, same regime, although a bit slower. Stirring as well of course, although not too often, more like every 10 minutes.

Next, the madder. I used ground madder root, not wanting to grind it myself and not wanting just to use the extract. The recipes generally agreed you needed about 25-37.5% if not even 50% weight of madder to weight of wool. I used 39g or so (spilt a little), that is, 30% by weight, and left it to soak for a while, then heated the bath up to 60-65°C for an hour and ten minutes.
It was then left to cool for a couple of hours. The wool was added, and heated it back up to around 58-64°C for an hour.
Then I took it out, cooled it and washed it clear before hanging up to dry.

Why the specific temperature I hear you ask?

Well, according to some websites, you shouldn’t heat it above 60°C or so because more of the browns are brought out into the dye bath. But according to another, you had to get to 60-65°C to get the alizarin, the specific red dye molecule, out into solution…

All definitely agreed that it shouldn’t be heated beyond 70°C because it’ll end up more brown than red, and some of the photos were quite a dull red-brown.
There was another thing which was interesting – one claimed that the dyestuff liked hard water, so I added half a teaspoon of quicklime, and a pinch of sodium bicarbonate. This didn’t seem to affect the pH much though, since at the start it was around 6.4. Yet by the end it was around 4.something, which is interesting and may be due to the different pH’s of the different dye molecules.

But the dyebath was still pretty dark red in colour…
I’m still not sure what is going on, unless something was wrong with the first pH readings.
Other sources online suggest you should add quicklime at the end of the dyeing, or that you should make the dyebath more alkaline to begin with.
A great deal of specific testing is required to sort out which is correct and which is not. What I’d really like would be to be able to test for concentration of alizarin or other organic molecules, but that would require a great deal more equipment e.g. for chromatography. Unfortunately I suspect I’m also a decade too late to salvage an old gas chromatograph from a university that is upgrading.

Anyway, admire the redness of my cushion cover. I can do more, still 60g of dye left:
Cushion cover drying no flash

I’ve also tried some wool and linen dyeing in the remains of the dyebath, with and without alum mordant, and one piece of wool at 80°C to see how brown it turns out. But that’ll be another post.