To answer your first question now days you normally cannot visually tell. The silver wash is gone and rarely does the small amount of silver show signs. The way this was figured out was to determine where the type was minted, pieces made in the city would be found in greater quantities in the city, the also seem better made. Later Metcalf did a metal study and found out the Constantinople minted coins had silver, the other minted coins did not .Michael Hendy did the same test and got similar results. For Constantinople minted tetartera the silver content was as follows roughly, pg 62 on DOCIV for precise results on each type. Alexius - avg 3% John II- 3-4% Manuel- 2.5% Isaac II- 1% Now for trachea average pg 45 DOC IV John II -6-7% Maunel 4-6% Isaac II 2-3% As for color it depends on the coin where it layed the last 800 years, I remember when the hoard in early 2000's came to light, silvered coins before that find were extremely rare but someone smuggled 30,000 plus coins on the market, then suddenly we all had silvered was trachea. Ok this coin has nothing to do with the conversation but I wanted to add it to the thread, A Hyperpyron of Isaac II, it is really attractive.