Chuck,
Sorry to be slow answering but I've been traveling most of this week. I'll take a partial stab at your question. I hope others and especially Guy will chime in. Guy does a real good job with his written descriptions of E. TN traits and has helped me a lot over the years.
Ken
"
I'm going to ask. What are the main characteristics that the trained and educated eye looks for when they say, "
First, there are 3 or 4 different schools within TN. I've studied what I consider to be the 2 in E. TN. Upper E. TN and Soddy-Daisey. To some the Soddy guns are part of the E. TN school but I consider that a school all to itself. Second, guns were being made in E. TN as early as 1790ish and in some places never stopped so the span of time is pretty broad.
For E. TN guns I look for several things.
Architecture - draw an imaginary line along the top of the comb. On an E. TN rifle it will most likely continue on without intersecting with the stock in any place. The obvious exception is the Bogle rifle.
Tang - most of the time upper E. TN tangs will be long and continue up and over the comb.
Soddy tangs will be long and more of a flat strap.
Triggers - Before the mass produced triggers started showing up most all TN triggers had the same look. The front trigger has that half circle boss and a well rounded rear trigger. Double set triggers are almost always the rule.
Compare that to a modern double set trigger.
They have a very concave area where the wrist meets the lock panels and the barrel breech.
Deep Crescent Buttplate.
Soddy Buttplate - Notice the height of the comb plate and the deepest part of the curve. The deepest part is near center on a Soddy rifle. While looking at this picture notice the release spring for the patchbox lid.
Upper E. TN - The comb plate is not near as deep as a Soddy. The deepest part of the crescent is more in the top 2/3 area.
You can also see the more typical box lid release made from an nail