An interferometric method for profiling the topography of a sample surface, said method comprising the steps of: (i) a first interferometric profiling step in which a sample surface is analysed by single-frame interferometry at a relatively low first magnification M1 to produce a map comprising pixels with planar (X,Y)-coordinates corresponding to the area of the sample surface, (ii) interrogating the pixel data obtained from the first profiling step by identifying pixel(s) which meet or exceed a Cut-Off Threshold which defines a height above or below the mean plane of the sample surface, and which also meet or exceed a parameter N NAP which is the number of adjacent pixels all of which meet or exceed the Cut-Off Threshold; (iii) interrogating the pixel data obtained from the first profiling step by identifying pixel(s) for which no z-coordinate has been recorded; (iv) generating a Low Magnification Frame File (LMFF) which comprises the (X,Y) coordinates of the pixels derived from steps (ii) and (iii); (v) a second interferometric profiling step in which the sample surface is analysed at a relatively high second magnification M2, wherein M2>M1, wherein only selected regions of the sample surface are analysed at said second magnification M2, wherein said selected regions comprise the features associated with the (X,Y)-coordinates of the pixels in the Low Magnification Frame File; and further comprising a step selected from: (vi) the step of analysis of the output of the second interferometric profiling step to differentiate between an intrinsic defect and an extrinsic defect; (vii) the step of assessing whether said sample surface meets one or more quality control standard(s) and/or one or more target property or properties; and (viii) the step of assessing whether said sample surface is suitable as a surface for subsequent coating. (i) a first interferometric profiling step in which a sample surface is analysed by single-frame interferometry at a relatively low first magnification M1 to produce a map comprising pixels with planar (X,Y)-coordinates corresponding to the area of the sample surface, (ii) interrogating the pixel data obtained from the first profiling step by identifying pixel(s) which meet or exceed a Cut-Off Threshold which defines a height above or below the mean plane of the sample surface, and which also meet or exceed a parameter N NAP which is the number of adjacent pixels all of which meet or exceed the Cut-Off Threshold; (iii) interrogating the pixel data obtained from the first profiling step by identifying pixel(s) for which no z-coordinate has been recorded; (iv) generating a Low Magnification Frame File (LMFF) which comprises the (X,Y) coordinates of the pixels derived from steps (ii) and (iii); (v) a second interferometric profiling step in which the sample surface is analysed at a relatively high second magnification M2, wherein M2>M1, wherein only selected regions of the sample surface are analysed at said second magnification M2, wherein said selected regions comprise the features associated with the (X,Y)-coordinates of the pixels in the Low Magnification Frame File; (vi) the step of analysis of the output of the second interferometric profiling step to differentiate between an intrinsic defect and an extrinsic defect; (vii) the step of assessing whether said sample surface meets one or more quality control standard(s) and/or one or more target property or properties; and (viii) the step of assessing whether said sample surface is suitable as a surface for subsequent coating.