Onion skins on four different mordants

It's been awfully quiet here at The Laboratory of Dr Me since I was lab-less (or, rather, homeless) during the summer and autumn (bought a flat, all went wrong, etc. etc. - but all ended up fine in the end). All of my materials for making things brown were in storage. We were reunited at the end of the year and I just managed to get one experiment in before 2011. My idea was to test one dye extraction (onion skins, of course!) on four different mordants: alum, tin, copper and iron. I decided against trying chrome for reasons discussed in my previous post.

The easiest way to do an experiment such as this one is to mordant each hank separately and then chuck them all into one big dyebath together to dye, and this is the method recommended in most books and websites. In my very first dyeing experiment, though, I found that you get a lot of colour contamination when you bathe hanks together - in particular, iron (which will darken onion skin dye drastically) is likely to drag down all of the other colours. So I dyed the hanks separately - which, of course, takes longer. In fact this experiment taught me two main things: firstly that mordants can indeed produce a lovely range of dramatically different colours, and secondly that four dye lots in one day is way too much. I think it took about 9 or 10 hours all in all.

Fabric: 4 x 100g wool
Dyestuff: 132g onion skins (4 x 33g)
Mordants:

• 8g alum (potassium aluminium sulphate) with 7g cream of tartar
• 2g copper (copper sulphate) with 10ml cider vinegar
• 7g tin (stannous chloride) with 8g cream of tartar
• 5g iron (ferrous sulphate)

First I boiled up 132g onion skins. Do you know how much that is? I do. It's loads.



I have two dyeing pots (never use a pot for food after you've used it for dyeing) so I did the mordanting and dyeing in two stages. First up were alum and tin. I've used alum a dozen times before but wasn't familiar with tin. My usual approach with alum is to dissolve it in a pint of hand-hot water before pouring this into the cold bath. I tried the same with the stannous chloride, which completely refused to dissolve in the hand-hot water. After stirring for ages I gave up and dunked it into the bath. The result: big bad precipitate.



What the hell! Put the yarn in anyway. The precipitate then settled on the yarn, rather like a snow globe. I wonder if this will lead to patchiness?, I wondered. And did it? Hint: yes.



The tin mordant dissolved beautifully by the time the temperature got up to about 70 or so. If you're planning to work with tin, I'd recommend dissolving it on the hob in the dye pot, then adding cold water once it's dissolved. At least, that's what I'll try next time.

Dyeing the alum & tin hanks held no surprises. It all went orangey as expected.



Next stage: copper and iron mordants. These behaved much like alum - dissolving easily in the hot water. But I don't think I'd appreciated how strong their own colours are. Here they are, five minutes or so since the yarn went in:



Here's the yarn after leaving the copper mordant bath:



And here's the other hank after leaving the iron mordant bath:



That hasn't even touched the onion skins yet. Of course, when it went into the dyebath its colour deepened a lot, as is the way with iron.

Here are the hanks drying over my bath:



And the finished balls of wool.



And what a lovely palette they make. The tin-mordanted wool, while definitely a lot patchier than the others (hard to see in the photo) is such a stunningly vivid orange - I had no idea that tin's brightening effects were so dramatic. It is definitely a bit scratchier than the alum, though, and that makes sense since tin is known to make fabrics brittle. I've heard that you can add a little tin to an alum bath to brighten the colour, which is definitely something I'll be doing in the future. Tin mordant is far more expensive than alum, so it's a good choice economically as well as practically.

Now I just have to decide what to make with these!