Dyers who grow woad will often find they have far more woad seeds than they could possibly need for sowing themselves or passing on to other dyers.
Some years ago I did some tests using ripe purple/black woad seeds in the dyepot and I was intrigued by the results.
This rather dark image shows the page from my record book where I have the samples from this dyebath. The upper (1) of each pair of samples is unmordanted and the lower (2) is alum-mordanted. The seeds produced an attractive green on alum-mordanted wool, and a more yellow colour on unmordanted wool. Perhaps the most interesting sample was the one modified in clear vinegar (acidic), which produced a pale pink on unmordanted wool and a deeper pink colour on alum-mordanted wool. An alkaline modifier gave lighter yellowy greens, copper intensified the greens and iron produced greyish greens.
Woad seeds can be used in the same way as most other plant materials and I would suggest using at least the same weight of seeds as fibres (100%). Simmer the seeds for about 45 minutes to extract the colour, then strain off the dye liquid, add the fibres and simmer them for about 45 minutes to an hour, or until the colour is deep enough.
Recently I collected a bagful of woad seeds for a dyebath. This time about half of the seeds I used in the dyepot were not fully ripe and were still green in colour, rather than purple/black. The colours I obtained this time were less interesting, suggesting that it is advisable to allow the seeds to mature fully and become black before using them in the dyepot.
From top to bottom the samples are: No modifier, + acidic modifier, + alkaline modifier, + iron modifier. For each category there are two samples: the upper one is unmordanted and the lower one is alum-mordanted. The shades are very similar to those achieved from the earlier dyebath using fully mature seeds, but considerably less intense.