PB;

Yes, that would be the black Dura Coat finish. Doing the math, your 12 X17 pan is 204-square inches (L X W)

and the 13 X 18 is 234-square inches, a difference of 30-square inches (larger) so, dividing 30 by 204 we get a 14.7 (call it 15%) increase in pan size, so if you're making one dough for one pan, you will need to increase your dough size by 15%. If you have dough left over after filling the pan, then you will need to go with using the "dough factor" method for calculating the weight of dough needed for the new pan size. In this case you would divide the dough weight used with the 12 X 17-inch pan and divide that number by 204 (the surface area) to get your dough loading factor aka dough weight per square inch of pan surface area. Now all you need to do is to multiply the dough factor by the square inches in your new pan size (234) and you will get the dough weight needed for your new pan. Here's a neat trick, put your dough formula into bakers percent and add up all of the percentages (you'll probably get something around 164), move the decimal point two places to the left so now you would see 1.64 and divide the total dough weight by this number, the result will be the flour weight needed to make your new dough size, once you have the flour weight the rest is easy to calculate the amounts of each ingredient. Or, you can just use the conversion tables.

Tom Lehmann/The Dough Doctor