The "normal" percentage only applies to the chance to craft, and only when you are high enough level to craft an item. this, for most skills, advances 0.2% per 0.1 skill.
If something requires 60 skill to make, even a +30% talisman won't let you make it at 59.9 skill.
The base "Exceptional" chance to make is (below 95 skill) your normal chance to craft -60%. So, if you are 55% chance to craft something, you are at -5% chance (display says 0) to make something exceptional. This ability ALSO advances 0.2% per 0.1 skill, but is calculated separately from normal skill chance (as a result, the normal bonus from a talisman does NOT raise your exceptional chance number)
However, unlike the normal crafting chance, the computer keeps track of the "real" exceptional chance when it would normally be negative, so if you stuck a +30% exceptional chance talisman on when at an effective -5% chance to make exceptional, you'd be 25% chance to make an item exceptional.
If one was 80% chance to make an item, below 95 skill, you are 20% to make it exceptional (plus whatever the exceptional bonus is).
From 95.1 to 100 skill, most items have their normal chance advance 0.5% per 0.1 skill, while their exceptional chance advances 0.2% per 0.1 skill.
The net result is that (without talisman) your chance to make exceptional is unmodified normal chance -45% (as opposed to -60% at 95 or lower skill).
Funky Numbers and exceptional chances.
One would THINK that, is such an instance of 80% success chance (20% exceptional), that you'd succeed 4 out of 5 times, on average, and that 20% of the items from success checks would be exceptional.
The math: 80% * 20% = 16%
So out of 100 attempts, one would expect 80 items, 64 of which are normal, 16 exceptional.
With a +30% talisman, that would be 80% * 50%, or 40 normal items, 40 exceptional items.
But, while logical, that's NOT how it works.
Apparently, the exceptional chance is checked in such a way that it is compared to the number generated to determine normal success.
Using the 80% normal, 20%+30% chance exceptional numbers from before, instead of being (80 items, 40 normal, 40 exceptional)
you get (80 items, 30 normal, 50 exceptional).
This does NOT follow normal associative, communicative, etc. rules for multiplication, so it is probably an artifact of the way the coding of the chance is made (after all, how many of you have had cheap pocket calculators before that said that 1+2*3 = 9, not 7?)
I think it would look something like this in the coding
Takes normal chance number (in this case 80%)
compares exceptional chance number (in this case, 50%, with the talisman)
Server rolls for item creation (number 0.1-100.0 generated). 0.1-80 item; 80.1-100 no item. It now compares exceptional chance number to the item creation roll.
A. If 80.1 to 100, no item created.
B. If the roll is over the exceptional chance, but low enough for an item to be created, then a normal item is made.
C. If the roll is under the Exceptional chance, then the item is exceptional.
This set-up makes exceptional items more common for sub-100% chance to make items, than multiplying the success chance by the exceptional chance would allow.
In fact, the difference can get really big for a GM+ smith.
Same base chance to make (80%) for a GM+ smith, means that the base chance for exceptional is 35%, not 20%. Add in a +30% bonus and it becomes 65%.
Using normal math rules, 80% * 65% would be 52 exceptional, 28 normal.
Using the code I suggested, you end up with 65 exceptional, 15 normal!
I made numerous runs of items to check this, and the latter seemed to hold true. In fact, as you get closer and closer to 100% natural (no normal bonus on the talisman), the more pronounced the effect becomes.
So, that at 95% normal chance (50% base chance for exceptional) with the exceptional chance raised to 80% by a +30% exceptional bonus only talisman, you end up on average with 15 normal, 80 exceptional, and 5 failures!
As a result, when you truly need exceptional items of a type you can't make 100% normal, it's best to use an exceptional ONLY talisman, as it actually reduces the number of normal rejects.
Example: 65% chance, 20% exceptional (GM skill)
With a 30/30 talisman: 95% chance, 50% exceptional = 45 normal (rejects), 50 exceptional, 5 failures.
With a 0/30 talisman: 65% chance, 50% exceptional = 15 normal, 50 exceptional, 35 failures.
If you're making a recipe item with a mid-range runic, where the single special ingredient is NOT consumed on a failure (any weapon recipe using the ML gems, for example), losing a bunch of ingots/boards on failures is a LOT better than losing those gems from normal quality ones you'll end up smelting anyway. Now, if you're burning a verite or valorite hammer, perhaps getting more successes might be more attactive (you might find someone interested in buying a non-DI weapon with good properties), but most other times, you're better off converving the gems for the next attempt.