To take the damage of the cylinder is very tricky,I am not responsible if you remove the blue off your gun.What I use is Maas metal polish,It is the least abrasive metal polish I have come across.I take a very small amount on my finger and rub it VERY gently over the area,ONLY use your finger no rags.It should gently lift the crud off the cylinder then I very gently wipe off the excess with a microfiber towel(like the one in your pic).This has always worked for me and I have never damaged the blue.I have used this method on Pythons,Pre 29's,etc.