The sur­face of met­al, glass and plastic ob­jects is of­ten char­ac­ter­ized by mi­cro­scop­ic scratches caused by man­u­fac­tur­ing and/or wear. A closer look onto such scratches re­veals iri­des­cent col­ors with a com­plex de­pend­ency on view­ing and light­ing con­di­tions. The phys­ics be­hind this phe­nomen­on is well un­der­stood; it is caused by dif­frac­tion of the in­cid­ent light by sur­face fea­tures on the or­der of the op­tic­al wavelength. Ex­ist­ing ana­lyt­ic mod­els are able to re­pro­duce spa­tially un­re­solved mi­cro­struc­ture such as the iri­des­cent ap­pear­ance of com­pact disks and sim­il­ar ma­ter­i­als. Spa­tially re­solved scratches, on the oth­er hand, have proven elu­sive due to the highly com­plex wave-op­tic­al light trans­port sim­u­la­tions needed to ac­count for their ap­pear­ance. In this pa­per, we pro­pose a wave-op­tic­al shad­ing mod­el based on non-paraxi­al scal­ar dif­frac­tion the­ory to render this class of ef­fects. Our mod­el ex­presses sur­face rough­ness as a col­lec­tion of line seg­ments. To shade a point on the sur­face, the in­di­vidu­al dif­frac­tion pat­terns for con­trib­ut­ing scratch seg­ments are com­puted ana­lyt­ic­ally and su­per­im­posed co­her­ently. This provides nat­ur­al trans­itions from loc­al­ized glint-like iri­des­cence to smooth BRD­Fs rep­res­ent­ing the su­per­pos­i­tion of many re­flec­tions at large view­ing dis­tances. We demon­strate that our mod­el is cap­able of re­cre­at­ing the over­all ap­pear­ance as well as char­ac­ter­ist­ic de­tail ef­fects ob­served on real-world ex­amples.