To check for henna that has metal salts check this link.
Posted by Faery Ring on September 30, 2004 at 16:44:09:
In reply to: Most of the henna powder from ethnic markets is harmless. posted by Faery Ring on September 30, 2004 at 16:41:24:
Of course it will require that you have harvested some hair and hennathat first. But if you absolutely must be certain than this is the
best way to check. I don’t know of any other. Maybe a laboratory
can test it but I am sure the cost would be prohibitive.
If you don’t have harvested hair you could try some henna paste on
raw silk and then put the silk into the peroxide+ammonia solution to
check.
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