Troubles with icons for custom contact sub_types

[myles]

To encourage appropriate use of sub-types I'd like to give them icons of their own...

But they are not showing.

First step for me is to check the format and sizing of the default icons - but I can't find them - so two questions:

1) where are the standard contact type icons located?
2) could someone confirm this is a valid relative path:

../../../default/files/volunteer_contact_icon.png

TIA

PS - version 4.5.2 hosted in Drupal 7