Jim, yes there would be chipping if it was cellulose putty. I used Magic Sculpt so it's a bit harder but normally I would use a corner of a file to score and then only scribe with a scriber. For the curves I use a PE saw.
Colin, if its in a plastic bag chances are it's a relic and molded before I was born. Even the picture depicts the nose wrongly.
Steven, the plastic surgeon says thank you.
I've done a bit just now by scribing and adding the screw heads with sliced styrene rod...
On close up scribing looks quite roughly done as my eyes are starting to blur a little.