From some dyeing list on Yahoo!

Using 4 oz of chopped weld with 1# of alum mordanted wool came out witha lovely but very pale yellow. Chalk was also used to "bloom" the colorbut didn’t do much.

One standard rule of thumb is weight for weight, and I have heard of as much as 4 weld: 1 dry fibre for a strong, oily yellow colour. It helps if the weld includes root and seeds.

I usually use 1 oz of weld for 2 oz of mordanted wool. This gives a veryintense yellow. The important thing is to simmer for about 2 hours with an alkali such as baking soda, washing soda or even a weak solution of sodium hydroxide. I also find that any grease in the wool reduces the colour considerably. Some wools dye better than others too.

I find weld a very strong dye with normally 50% of weld to WOF. Ammonia added to the end of the dye bye will turn a soft yellow into a briliant one. If you are getting a pale colour then it could be you have picked it too early. I reckon that you get the most colour when the weld is starting to turn to seed but still has some flowers on and all its leaves but the leaves are starting to turn slightly past their best. Since I wrote my dye book I have come across recipes where you pour boiling water onto the leaves a couple of times but when I did this I found a pale colour – I think this might jsut be like madder that one is extracting different dyes in the weld as it has two so you may find that different methods of extraction help too. Oh and fermenting it helps as it goes on producing dye for days but you may find the smel gets a bit offensive ( although posssibly not as bad as Janes indigo yeast.ammonia vat and madder soaked in yoghurt! )

Have ready a bucket of very hot water with some ammonia in it ( about 1/4 cup to the 6-8 litres) and put some weld dyed wool in straight from the dyepot…..you get beautiful neon yellow!