Thorbjorn Fargeron

this is excellent work. well done. i love the detail on your reproduction from the photo, and it really has a solid Norse feel to it throughout most of the image. sometimes it's hard to differentiate Norse from Celtic art, and i think you've pulled it off.
you might darken the borders of the dogs on the brooch, since they get a little lost in the details. other than that, there's really not much i would recommend to change. you could go with a little more detail for the dogs (or maybe deer?) on the left and right, and possibly shoot for a greater level of symmetry with the two lateral designs on the bottom. but really, these are all possibilities for change, not necessarily for improvement.
the one other thing is, if you have access to photoshop, you could clean up the solid black areas a little for the digital version. i run into this issue often myself - something that looks solid-color on paper turns out streaky once it's been scanned.

again, well done!