[alt-photo] Re: odd tintype observation

[etienne garbaux]

Christina wrote:

>I got the trophy metal plates (black painted aluminum) from a trophy store

I can't comment about the particular plates you got, but aluminum 
engraving plates are generally anodized (anodizing is an electrolytic 
oxidizing process).  The oxide layer is dyed black (or yellow, blue, 
red, etc.).  It is a bonded (not applied) finish.  It is almost 
always given a hydrophobic sealing as the last process step, to 
improve environmental resistance.  Before it is sealed, anodizing is 
quite porous and holds many kinds of coatings well.

Best regards,

etienne