For most line art you would now be ready to convert from Grayscale to Bitmap mode. But if needed, you still have the ability to refine specific areas of the line art by editing the grayscale image. To do so, make the image active by clicking on its name in the layers palete. Here are some ways to refine the image further:

To increase fine detail in shadow areas—Brush across area with the sharpen tool.
To make lines thicker or fix broken lines—Brush across area with the burn tool using the shadow setting. If that doesn't do the trick try the History brush (remember the Snapshot that we made of the original scan and then assigned the History brush to it?) with the blending mode set to Multiply or Darken.
To make lines thinner—Brush across areas with the Dodge tool using the Highlights or Midtones settings. If that doesn't do the trick, try using the History Brush with a blending mode set to Screen or Lighten.

Tip:
If the image is going to print on newsprint, you might use these techniques to open up the detail in the shadow areas of the image even more than normal. This would allow for the tendency of newpaper printing to fill in the detail in the dark areas of an image.

(The History Brush will use the Snapshot "UnsharpVersion", that we created and assigned the history brush to earlier in this tutorial)