The unnatural hair colour question is not a duplicate

Question

This question about dyeing hair into unnatural colour using medieval technologies was closed as a duplicate of this question asking about dyeing red hair into a natural colour in a similar setting. However, these questions require very different answers due to several considerations explained below.

1. Unnatural hair colour is a two-step process: Bleach, then dye

   Natural colour does not require bleaching. There is a wide range of natural hair colours that can be easily achieved without extreme chemical processing. For the natural hair colour question, the easiest and least damaging option would be dyeing hair darker and changing its shade into brown.

   Unnatural colour requires bleaching in all cases, except when the base colour (the natural hair) is very light blond. Dark hair is very hard to dye and unnatural colours like blue, yellow, green, bright red, orange, and so on are impossible to achieve without bleaching. This is precisely the reason why the majority of sheep raised for wool is white: It increases dyeing options. Wool from non-white sheep is rarely dyed and is often spun as it is.

   Even highly pigmented dyes do not produce unnatural colour results when applied to dark hair (medium brown and darker), they only result in a change of hue. The darker the base the less noticeable this change will be.

2. Limitations of medieval hair dyeing options

   Medieval hair bleaching options were very limited and did not produce results similar to hair bleaches of today. The most popular bleaches were lye soap and ammonia. In addition to these, people would expose hair to the sun to lighten it (sometimes using lemon juice and similar remedies to increase the bleaching effect). All of these approaches have 2 things in common: 1) They are not capable of colour lifting to the same degree as modern bleaches (it is impossible to achieve very light shades unless the hair is originally light); 2) they seriously damage the hair (the hair becomes prone to breakage; overprocessing can even make hair so fragile that it breaks at touch).

   Many colour dyes, while probably not highly toxic, are still damaging for the hair. For example, woad dye (blue plant-based dye) is known to damage protein-based fibres and should be used with great care. It is possible that some (if not all) formulations of woad dye cannot be used on bleached hair at all since it would lead to extreme damage and full loss of hair length due to breakage.

If we consider these 2 points, the answers to the unnatural hair colour question are limited to dyes that:

• are available in the Middle Ages;
• are non-lethal to humans (toxic dyes where toxicity accumulates over time are fine since lead makeup was a thing for millennia);
• can be safely used on bleached hair (this is probably the greatest limitation);
• produce unnatural colours when applied to the yellow-orange medium blond base (this would be the average result for bleaching in medieval Europe).

This is a different set of dyes compared to the natural hair colour question which looks for the following:

• are available in the Middle Ages;
• are non-lethal to humans (toxic dyes where toxicity accumulates over time are fine since lead makeup was a thing for millennia);
• reduce or mask red pigment in the original hair;
• produce natural hair colour when applied to a red base.

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Notes:

1. This is not my question

2. This is not a perfect question, but let's stay focused on the duplicate issue.

3. Please note that the accepted answer is not correct: Not all dyes that can be used on white wool can be used on human hair.

Answer 1

Some unnatural hair colors would require prior bleaching. Others would not. Indeed, nothing stops anyone from coloring their hair without bleaching — and the act of bleaching is not intrinsically required for the question. Said another way, I don't believe the need to previously bleach hair would change the answers.

On the other hand, The two questions are each asking for lists of naturally-occurring dyes or dyes available via the technology of the medieval era. I agree that the former question is specifically asking for elements that would lead only to natural hair color.

What would be realistic options to change hair color to any other natural hair color?

Unfortunately, the current question is badly asked. The title makes it sound like it's a duplicate of the previous question, and the only hint that it's not comes from bullet #2.

The current colour is a blue-ish hue, but that's definitely not permanent- It could be any unnatural hair colour.

I believe the question should be re-opened, BUT...

1. I believe the OP should have their attention drawn to how the question should (frankly, must) be improved. I have sympathy for the close voters. Yes, we should all be responsibly attentive when a question is asked. But it was very easy to overlook the differences between these two questions.

2. I believe it's not valuable to include the answers from the earlier question in the new one. In other words, the OP should be specifically asking for non-natural hair coloring solutions. No blonds, reds, browns, or blacks of any shade. Ideally, the OP would link back to the earlier question to indicate that those answers are found there.

3. I think it would improve the question to ask only for solutions that would not harm the person. I've no doubt that there are compounds that could dye hair all kinds of interesting colors — so long as one didn't mind their scalp being burned, or being poisoned, or contracting cancer or some other problem. The question could allow these so long as the OP invited respondents to indicate whether their solutions were safe to use and, if not, what would happen and how quickly.

4. It would help a LOT if the title actually expressed the specific question. Something like "Can unnatural hair color be achieved during the medieval period?"

Answer 2

This again?

From SE Meta: How should duplicate questions be handled?: When are two questions considered duplicates?:

Questions may be duplicates if they have the same (potential) answers. This includes not only word-for-word duplicates, but also the same idea expressed in different words.
Questions asking about the same aspect of the same concept, but with different examples, may or may not be considered duplicates. It depends how easy it is to figure out one example from the other. If it's only a matter of changing one small part of the question (e.g. in the case of coding sites, some numerical values or some variable names), they're duplicates.

As firmly established, these two questions not only have the same potential answers, the latter question was explicitly answered in the original across multiple replies. They also ask their questions in nearly the same words.

It continues:

If understanding why the questions are at all related requires a detailed explanation, the questions aren't duplicates, merely related.

The question was closed and it has taken multiple detailed explanations to attempt to argue they aren't related, inventing criteria neither asker signed off for in their questions, and at one point urging users to 'read between the lines' of one question (but not the other).

Further, under Which question is the duplicate?:

The general rule is to keep the question with the best collection of answers, and close the other one as a duplicate. If the selected target question is unanswered, the system won't even let you pick it as a duplicate target*.
If one question has great answers but bad wording, and the other has poor or no answers but great wording, edit the badly-worded question and close the other one as a duplicate.
If in doubt, close the more recent question as a duplicate.

Ergo the newest one should be closed and remain closed.