Your base chance to make a blacksmithing item is 0.2% per 0.1 skill beyond the point where it claims you can start making them.
Your chance to make an item exceptional, for skill under 95, is chance to make normally -60% (without a talisman, but does include ASH).
At 100+ the exceptional chance is normal chance - 45%.
Between 95 & 100, as an artifact of the pre-powerscroll system, the exceptional chance gets an additional +0.3% per 0.1 skill gained between the two points (creating the difference between the under 95 and over 100 amounts).
Adding a talisman:
A Talisman WILL NOT give you a chance to make something normally, if your unmodified normal chance is 0%
A Talisman's normal Crafting Bonus DOES NOT MODIFY the Exceptional chance.
A Talisman's Exceptional Bonus does add to the number for the exceptional bonus, even if the exceptional chance would normally be negative. As a result, at 55% normal chance (where you would be -5% chance of success), a talisman with an 18% exceptional bonus will give you a 13% chance to make exceptional.