Fixing the "oops"

Yesterday's post about proofreading raised the topic of how to handle the mistakes you find.  
Let's define "mistake" as pigment that doesn't belong where it is on the page.  There are several ways to handle a calligraphy mistake. 
First do no harm.  I can't emphasize this enough; don't make the situation worse by over-reacting.  Spend 10 minutes to assess the error, relax, remind yourself that everyone makes mistakes. 
Assess the limits of your materials: What kind of ink: is it made of pigment or dye?  What kind of paper: soft and spongey or coated to keep the ink from soaking into the fiber?     
Level of scrutiny vs magnitude of error: is this a small glitch or something fundamental to the whole piece?  how close will the reader be to the page?  Is this original art or is it for a print?    

Hold the paper against a mailing tube or... 

... roll the paper around itself. 

In my recent mistake--the extra comma after the word "glance"--several factors were working for me: the paper had a hard surface already, called hot press, plate finish; it was made harder by a thin coat of sizing; the ink had dried to a thick layer on top, scarcely soaking into the paper fibers; the comma was sitting in white space, all by itself.  These allowed me to put a fresh blade* in the X-acto knife, curve the paper over a cylinder, and shave the ink off.  
*either curved #10 or pointed #11

With the blade parallel to the paper, peel up the smallest possible surface layer, then trim it off at a right angle to the first motion.