The invention relates to a method for machining substrates (1), wherein a) a substrate (1) is provided, comprising: - an electrically conductive coating (2), - at least one insulation line (3), - at least one first (2.1) and second coating (2) sub-region (2.2), between which an insulation line (3) runs, - optionally at least one defect (3.1) with a proportion of less than 10% of the total surface area of the insulation line (3), b) a first electric contact (4.1) is connected to the first sub-region (2.1) and a second electric contact (4.2) is connected to the second sub-region (2.2), c) a voltage Un is applied between the first electric contact (4.1) and the second electric contact (4.2), d) a measurement is taken to detect whether an electric current is flowing between the first (2.1) and the second sub-region (2.2), and e) if a current is flowing, steps c) and d) are repeated with a voltage greater than or equal to Un until a current can no longer be measured in step d).
