Light Fastness Experiment

 I have heard and read many people comment about how "fast" a dye is, that is, how reliably the dye will stay on the fabric when subjected to washing (washfast) or sunlight (lightfast). Or, conversely,  how "fugative" it is; how likely a dye is to run when washed, or fade when left in the sun. I worry when I use natural dyes, about how long they will last, particular if I am planning to use the fibre or fabric for a project. I worry even more when the dyeing is done for someone else!

There have been conflicting reviews about how fast some dyes are, so I decided to do a little test of my own, using small swatches of wool and silk.  It's pretty rudimentary; I just glued them on a piece of paper with the dye written above it and left them hanging in the living room window for two weeks.  We get direct sunlight at peak hours.