Several people have asked me how I get such clean look with my tangles. The secret is PhotoShop or PaintShopPro. I scanned everything on a flatbed scanner at 300 dpi. I open the file in one of the two programs. (I was a PaintShopPro user before I got PhotoShop so sometimes I go back to it.)
First I adjust the brightness and contrast depending on what kind of paper I drew on. You will have to play around with it to see what looks better. The next step makes the biggest difference and a lot of people do not know about this. I do a gamma adjustment. This gives the image a boost. The lines become stronger - not a lot, but enough to enhance the image.
The last step is going in and "erasing" any accidental marks I may have made. Knowing I can do this, makes tangling less stressful. If I make an "oops" I don't panic because I know I can correct it later.
One time I spilled a bit of coffee on one of my drawings, and I was able to fix it in PhotoShop. If Hollywood can do, so can I!
Here is the original scan of the fish I made for the book, The Art of Zentangle. Below it is the image after I used one the programs. This was a pretty clean drawing before I scanned it so I didn't have to make a lot of adjustments.