"How To" Repair Paint Chip
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Some guitars are painted with a solid colour whilst other are clear coated with lacquers, if you chip the paint on a clear or tinted surface you can do what is called a drip fill repair.

This guitar has taken an impact to the butt, this has damaged the wood and removed the solid paint.

Time to repair approx 4 hrs over 4 days (Paint drying times)
Sand until the area is smooth to the touch.
To start with, we just want to build the area of concern back up, so apply some low tack tape around the perimeter of the repair.

Make sure all exposed paint has been lightly scuffed, you can use 400 grit for this.
Applying 4 coats of black over the space of 2hrs, allow to dry overnight.
With 400 grit sandpaper, I resand all my exposed areas, this flattens our paint and overcomes any sink back that may have happened.
Again another 4 coats of black paint. Allow to dry overnight.
Remove our tape and assess the area of repair for small holes, missed paint areas and so forth, if any of these exist repeat the step's above.
A side view.
Using a polished flat piece of steel, I slowly scrape away the paint line where my low tack tape was.

Follow up clean the whole surface.

Lightly scuff the surface before applying clear. 400 Grit sandpaper is fine (forgot to take a photo of that one)
Damaged bottom area - Solid Paint

If damage is in clear lacquer, please also refer to this tutorial link
Using 220 grit sandpaper on a backing block, we smooth all the damaged area out.
Using some shellac on a rag, we seal the wood pores in preperation of paint work.

Attached link for shellac mixes.  
With no masking tape, apply 3 coats of clear over the area, do not worry about the overspray.

In this photo you can see the overspray from my clear paint.