I've posted this finishing process before (May 2009,I think) but it is so vitally important, that it's worth a repeat as I work this process on this quilt. I've worked in a number of judging rooms and can't count the number of times I've heard judges see and comment the edges of an art quilt as not straight. The quilt is unlikely to ribbon if this is the case. Getting this part right is the first reason we blocked this quilt. Now that the quilt is flat.... we need spend time getting it just right. I first line up the quilt on a gridded mat and select one side to set the first side. I generally use a drafters T-square to mark this line with a marking pencil before cutting off excess.
Once marked, time to rotary cut.
Time to use that old.. measure twice ( in this case 3 times).. cut once. from the freshly cut edge, measure at upper, middle, lower edges to get the opposite side marked, then cut.
The same need be done for the sides at a right angle to what is done, making certain the first side cut is really at a 90 degree angle to the already cut side. Measure measure measure.... then cut.
Believe it or not, once all four sides are trimmed... again measure for the exact same measurement at upper, middle and lower edges of (in this example the long side of the quilt.)
Now measure 3 ways on the opposite side.
Hairline sized corrections might be needed but party and move on if all measurements are good. YEAH!