Tiffany. How much does damage devalue a piece of L C Tiffany - Favrile?

I have a wonderful L C Tiffany- Favrile Blue iredescent glass vase. It has a small chip on the rim. Can hardly be seen but it can be felt. Have another piece where somebody professionally made a hole i'm assuming for a light, just enough for a wire. Understandably it will take a away from their worth. However, with some items that can be 90% and sometimes as little as 5%. Does anybody know of approx instant % devaluation or have any suggestions of where I should go from here.