In my book, Helen dyes her hair twice to disguise herself. The first time with a home-made concoction that turns it black or brown, and the second time a proper dye which turns it red. The challenge is finding a home-made dye which Helen, as a child of twelve, would be able to get her hands on, mix, and apply without help. Now, she does have access to information that a normal twelve year old wouldn't, and so her knowing how to make dyes isn't my problem. My problem is that I personally have no idea what went into producing a good dye during the period in which Helen would have lived, which means that I have to do research.
And the process that was used during antiquity to dye hair is mind-blowingly awesome in its simultaneously simplicity and complexity. You see, during antiquity, Greeks and Romans and Egyptians dyed their hair using nano-technology without even knowing it! Of course the downside is that it required lead oxide, which probably didn't do much for their health. The other problem is, how the heck would Helen get her hands on lead oxide or lime? And that kind of dye process is absolutely permanent--which is, of course, what Helen is going for, but not at all helpful to ME for later events, and Homeric Greece was certainly not Antiquity. I can believe that these kinds of techniques were known in Egypt, however, and in the east. Troy by all accounts seems to be very rich in these kinds of things-- a center for trade. But Helen at age 12, working under the radar, can't really engage in trade at this juncture.
Now there are a variety of pigments that were available to people in those times. Umber and Ochre for browns, reds and yellows, Bone and Carbon blacks, for, well, black for certain. (Incidentally, this webpage is kind of AWESOME for tracking pigment use through history.) But could any of these pigments be made into dyes? I'm thinking it would require some kind of solvent (and I'm totally wishing I had blond hair of my own that I could trim and try mixing dyes in my kitchen sink about now), vinegar would be a good one, or possibly even just wine or water. Helen could easily get her hands on any of those, but I have no idea how permanent that kind of dye might be, if at all.
But the only information I've been able to find on making ochre based dyes involves soy milk as the bonding agent. Earliest records of soy milk do not stretch back to Mycenaean times, even in China. I know cow's milk has a similar amount of protein to soy milk, but I'm not sure it has the same enzymes to allow the bonding-- or it might require the addition of an acid to activate them (like Vinegar or wine, I'd imagine, though I have no idea how the chemistry would all work out), or maybe egg would do. I have a feeling that even Helen, with her working knowledge will be spending quite a bit of time engaging in trial and error tests. I hate when my character is smarter than I am!
Late in the game I did finally find something that could be a practical and easy to make dye for Helen's hair, mostly by luck and persistence through wikipedia--walnuts! Boiling the fruit of the walnut tree apparently makes a dye which will darken as it oxidizes. Somehow I have a feeling that the adventures in milk and vinegar are now over for Helen. All she needs is to collect some nuts! Believe me-- the answer to this question did not come soon enough.
After all this, the second instance of Helen's ventures into hair dye is much, much simpler to handle. Henna makes a very simple red dye, no tricks involved, and it's something that she could easily buy or trade for now that she's not doing it in secret. In fact, it's probably something she could get from Troy, which works conveniently with the rest of my story when all is said and done.
On the plus side, I did learn how to make Casein Paint. Seems pretty simple, when all is said and done. Hooray for useless information I will never use found in the search for the information I actually NEEDED.
What was your last research time-suck? Is there anything that you tried to learn for a book, but could never find the information for?