Recently we developed methods to evaluate surface crystals in Cheddar and hard Italian-style cheeses, and internal crystals in Cheddar, Gouda, and Parmigiano Reggiano cheeses by powder X-ray diffraction (PXRD). However, new sample preparation techniques are needed to analyze surface crystals of washed rind cheeses because of the complex nature of the surface smear. Our objectives were to develop repeatable sample preparation protocols for smear evaluation by PXRD and to validate the protocols by single crystal X-ray diffraction (SCXRD). Initial efforts to evaluate crystalline inclusions in smears involved scraping the surfaces of 3 washed rind cheeses with a spatula and loading them onto PXRD slides. Fresh samples were used deliberately because ikaite (CaCO₃·6H₂O), which in cheese has thus far only been observed in surface smears, decomposes in the presence of acetone. Diffraction patterns showed limited repeatability between repeated measures when data collection was performed in succession at roughly 25 min intervals. The lack of repeatability was found to be an artifact of sample desiccation during data collection. To prevent drying during data collection, 2 modifications were investigated; sample slides were coated in a thin layer of immersion oil, and alternatively allowed to air-dry before pulverization in a mortar. PXRD data collected using both PXRD method modifications revealed that all 3 smears contained ikaite and that one of the smears also contained struvite (NH₄MgPO₄·6H₂O). The presence of ikaite and struvite was confirmed by single crystal x-ray diffraction (SCXRD) in the corresponding cheeses. It appears that smear material used in PXRD requires additional prep due to its extensive loss of volume upon drying, which causes diffraction artifacts. As confirmed by SCXRD, both modified PXRD methods provide valid diffraction data on the identities of crystals present in smear samples. Although SCXRD is a superior method for identifying the single crystals from surface smears, a reliable PXRD method is useful because powder diffractometers are typically less expensive, more widely available, and require less training to operate.