Do our instrument tiles have any expiration or re-certification date?
HunterLab provides the date that the tiles were calibrated, both on the label on the tile and the data sheets for the tiles. HunterLab does not publish an expiry date for these tiles.
ASTM E1164 says that the instrument user must assume the responsibility for obtaining the necessary material standard for calibration of the instrument. We have seen users set re-standardization intervals from as short as 6 months to as long as 5 years. The material the tiles are constructed from is very durable and stable in color and we have seen tiles up to 10 years old that still produce color that is nearly identical to their original color, as long as they are in good condition and well taken care of and undamaged.
You might want to consider the difference between tile calibration and instrument verification. If you are measuring in transmission where the top of scale is a 100% line created by completing the sphere diffusion by placing the white tile at the reflectance port then the calibration values assigned to the tile do not have much meaning. If you are measuring in reflectance where your reported values are a ratio of the sample reflectance compared to the calibrated reflectance of the white tile then the tile values carry more importance. In either instance the instruments wavelength accuracy is critical to producing accurate measurements. ASTM E275 describes the method to measure the performance of the instrument. HunterLab does recommend that instrument performance be verified at intervals not to exceed 15 months, but the end user can use either their own procedures following E275 or have HunterLab perform this type of test.