Heike Bödeker asked

> Just for curiosity's sake: is the percentage of tyrosinase then
> what makes the difference between types of black hair that display
> a reddish vs. a blueish shimmer when held against the light? Or
> what else is responsible for these (sub -?) types?
>
> Thanks in advance.

Heike, the best study that I know is "Quantitative analysis of
eumelanin and pheomelanin in hair and melanomas", by S. Ito, K.
Jimbow.

"In this study, a method is provided for analyzing quantitatively the
content and the class of melanin pigments in the tissues, e.g., hair
and melanoma. The method is simple and rapid because it does not
require the isolation of melanins from the tissues. The rationale was
that permanganate oxidation of eumelanin yields pyrrole-2,3,5-
tricarboxylic acid (PTCA) as its major pyrrolic product, which may
serve as a quantitatively significant indicator of eumelanin, while
hydriodic acid hydrolysis of pheomelanin yields amino-
hydroxyphenylalanine (AHP) as a specific indicator of pheomelanin.
The degradation products, PTCA and AHP, were determined by high-
performance liquid chromatography. Sepia melanosome-melanin and
synthetic 5-S-cysteinyldopa-melanin served as reference standards of
eumelanin and pheomelanin, respectively. Our method provided data
that corresponded well to the content and class of melanins in normal
hair. Based on this control study, it was found that the melanins in
the melanosomes of both B16 and Harding-Passey (HP) melanomas were
eumelanic and that the melanin content in B16 melanosomes was more
than 10 times higher than that in HP melanosomes, though these two
melanosomes revealed distinct colors and ultrastructures, i.e., brown-
black, eumelanosome-like granules in B16 and reddish- or light-brown,
pheomelanosome-like granules in HP."

PMID: 6833784 [PubMed - indexed for MEDLINE]

It would seem that the "blue black" hair you speak of tends to be
predominantly or exclusively pheomelanins. The addition of eumelanin
adds the reddish tinge.

Hope this helps

Regards

John