Abstract: A chemical characteristic of a material is measured using a calibration unit and container for holding a sample of the material. The calibration unit has a front portion and an imaging background positioned behind the sample and viewable through the container and the sample of the material, wherein a portion of the sample of the material is positioned in front of the imaging background so as to form a sample imaging region. A calibration strip extends along the front portion, which includes a location marker and a plurality of calibration indicia of differing colors. A computing device captures an image of the calibration strip and the sample imaging region. A calibration step is performed using the calibration strip to generate a calibration model, which is applied to the sample color vector to generate a calibrated sample color vector.