In these grey days of winter I've found myself dreaming of rainbows. Okay, if I'm honest I'm often dreaming of rainbows, and one of my favourite things to do is create rainbows with natural dyes (see this post!) There are many ways to do this, but often it will include some kind of overdyeing.
Overdyeing is just what it sounds like - taking a previously dyed fibre, and dyeing over it with another dye. It is just one way to extend the colour possibilities of your precious dyes (other methods include post-mordanting and shifting the pH), but it's a very simple and straightforward way, since most of us have experience with mixing colours using paints, going all the way back to primary school.
In general, the colours will react the way you expect them to - a pink overdyed with yellow will yield orange, and and yellow overdyed with blue will yield green. But don't be afraid to experiment - back in the days of fingerpainting, orange plus blue would inevitably turn to some kind of unappealing brown - but overdyeing the soft peachy orange hues of madder with the blue of indigo will often produce a gorgeous kind of mauve. It's a purple with a brown or grey undertone, as opposed the clear secondary purple of cochineal overdyed with indigo.
If you are using two mordant dyes (i.e. cochineal and osage), it doesn't matter which dye you use first. However, it is recommended that you use the higher percentage of mordant. Most recipe will list mordants as a range (i.e. use alum at 12-20%), so if you are planning to overdye, then use the 20%.
If you are a beginner dyer and planning to overdye with indigo, I feel that it's easiest to begin with the mordant dye, then overdye with indigo. The indigo tends to overpower other colours, especially yellows, so if you're trying to make green, you can see how many indigo dips you need to get a true green. Too many and it very quickly turns to turquoise. However, if you are an experienced dyer, there are couple reasons why you would want to dye the indigo first, including the fact that mordants are acidic and will help to neutralize the alkalinity of the indigo dyed fabric. You can find more about this and the other considerations in this fabulous and highly recommended book.
But as always, and especially if you are a beginner, I encourage you to just experiment. There are so many possibilities - you can even overdye commercially dyed fibres (have a shirt that you don't love the colour of? Overdye it!) It is possible to achieve all the colours of the rainbow with just three dyes - a pink/red such as cochineal, a yellow such as osage, and of course blue from indigo.
I am also now selling my two most popular beginner dye kits as a bundle - the Make a Rainbow bundle (US customers can order with free shipping from Etsy). This is how I made the rainbow in the photo above. From left to right, the samples were dyed with logwood, indigo, osage overdyed with indigo, osage, madder and cochineal. With the two kits, you get all the dyes, mordants and reducing agents to create your own rainbow.
And this week, I'm also having a giveaway of these two kits - head over to instagram to enter.