[Histonet] unknown Black pigment puzzle

[Mildred Fail]

Hello all,
       We have a skin punch biopsy containing a  black pigment we are trying to identify.   
Negative for Fe
Negative for Copper
No change with Ammonium Sulfide
Remains after melanin bleach
Remains after treatment with concentrated Sulfuric acid
Remains after treatment with potassium ferricyanide/hypo solution
Is removed by treatment in Lugol's Iodine, followed by hypo, but after this treatment what appears to be crystals are left in several areas  in a linear pattern. These do not appear to be Iodine crystals.
The patient did have acupuncture treatment, is it possible this is silver pigment? From the needle? Something else as simple as a splinter?
Any help would be greatly appreciated
Thank you
Rena Fail