Dear Laurie,
We strongly recommend conducting an optimization test in order to to improve the data collection quality and future model performance.
In order to reduce the variance, we would recommend the following:
1. Consistent experimental set up: using identical distance from the sample during the scanning process, constant temperature and ambient light.
2. Grinding or chopping the samples in order to increase homogeneity.
3. Pressure: the suggestion to put pressure on the sample may be effective, but glass will cause specular reflection. You can try to press the sample and then release.
Keep us updated!
Ayelet,
The Consumer Physics Team