Anyway, my method was the following: I measured 50 grams turmeric powder, dissolved them in warm water and I added 2 spoons of salt (no iodine type). I then added 100 gram wool that I already left to sit in water for around 2 hours. I put the pot on the fire, slowly raised the temperature to around 70- 80 Celsius degrees and left to simmer for around 40 minutes. I left the dye bath to cool with the wool still in. When it was cool, I removed the wool and added the next skein, this time 100 grams of wool pre-treated with alum. I repeated the procedure as before. When the dye bath was cool I removed the second skein and saw that there was still lots of color. I thought I might as well see how much more wool can I dye with the exhaust bath so I added another 200 grams wool and repeated as before.
So, what are my results: the first skein (no mordant) was a really nice strong dark yellow. The second (Alum mordant) was a lighter yellow but still a very strong vibrant color. The skeins that I dyed in the 3rd exhaust bath were almost neon yellow. Was I happy with the colors? Oh yes! Did I let them dry in the sun? Yes, I did. Did they changed color? Yeap, dramatically even. And the most dramatic changes I observed for all the skeins that were pre mordanted with alum. The strong vibrant almost neon yellows faded incredibly fast to a duller yellow pinkish shade. Such a big disappointment…
And so I tested and verified that the article I read was perfectly correct in assessing that alum and turmeric equal poor light fastness. And now that I also saw how dramatic the change in colors can be due to sun exposure I am not so sure I will use turmeric anymore. Or if I will do, I will only use un-mordanted wool which I will use for some home accessories, not for items that will spend a lot of time outside in the sun. Oh yes, and I will definitely use roots and not powder turmeric...