This looks really good... I am excited to see the whole peice unfold.
Scanning will always pick up some grit , to where you will need to do a little clean up in a photo editor unfortunately. Try cleaning the glass, and making sure any graphite smudging is a s clear as possible to help reduce it.
Online in the above pics, the locomotive looks good, its the negative space around it that appears to have unwanted grit, shadowing.