## 2 Materials and Methods
### Sample Preparation
#### 2.1.1 The Manufacturer's Choice  
Based on well-established pharmaceutical processes in producing pills [25; 26; 27; 28; 29; 30; 31; 32] or as commonly known from FTIR spectroscopy [33; 34; 35; 36; 37; 38; 39; 40], the following method is adapted for preparing samples for diffuse reflectance studies. Figure 1 illustrates the overall design for the powder press. Figure 1: (**a**) Cross section through the assembled powder press. 1: bottom plate, 2: ceramic slice, 3: bouncing plate, 4: sample ring, 5: cover plate, 6: target, 7: funnel, 8: cylinder, 9: screw. (**b**) Photograph of the powder press components. 1: bottom plate, 2: ceramic slice, 3: bouncing plate, 4: sample ring (left: 10 mm hole diameter, right: 20 mm hole diameter), 5: cover plate (left: 10 mm diameter, right: 20 mm diameter), 6: target (left: 10 mm diameter, right: 20 mm diameter), 7: funnel (left: 10 mm hole diameter, right: 20 mm hole diameter), 8: cylinder, 9: screws, 10: recoil-free hammer, 11: spatula, 12: powder sample. In contrast to pharmaceutical applications, the investigated materials (particles) are often just loosely adhering to each other and hence require additional stabilization for support. This is provided by a sample ring (4) which remains around the pellet throughout all optical investigations. A clean ceramic plate onto which the powder sample is pressed by means of a tappet ensures a matte finish to the sample surface. The safest method to remove these highly fragile pellets from the powder press is to disassemble the press itself to ensure minimal stress and shock to the sample. This modular approach can be realized by assembling the components listed below and shown in Figure 1:  
1. Stainless steel bottom plate. 2. Ceramic slice (glued on the bottom plate by a two-component adhesive). 3. Stainless steel bouncing plate (for fixating other components). 4. Stainless steel sample ring (depending on the available amount of powder we suggest a diameter of 10 mm to 20 mm and 4.5 mm depth). 5. Stainless steel cover plate (suitable for fitting the sample ring). 6. Stainless steel tappet (matching the funnel). 7. Stainless steel funnel (for inserting powder and directing the tappet). 8. Stainless steel cylinder. 9. Aluminum screws (to affix the other components. Aluminum is used in order to reduce wear of the adjacent components). 10. Recoil-free hammer. 11. Stainless steel spatula (for filling in the powder). 12. (Nano/micro) powder sample. The preparation of samples, including the assembly of the powder press, follows the recipe given below to construct the setup presented in Figure 1.  
1. Let the tappet slide in the funnel on a clean planar surface (e.g., table, but not on the ceramic slice) and mark the position on the tappet at the upper end of the funnel. The ceramic slice itself must never come in contact with the tappet or other components as this would cause contamination of its surface which are relayed onto the sample. 2. Affix the clean and dry bottom plate (including the ceramic slice) to the bottom of the cylinder, either by a screw thread or a plug connection. 3. Place the sample ring on the ceramic slice and cover it with the bouncing plate. 4. Fix the bouncing plate with the screws through the cylinder's threads. 5. Screw the funnel into the sample ring. 6. Pour sample powder through the funnel. 7. Gently tap the powder with the tappet by hand. 8. Fill sufficient powder into the funnel to allow compression by hammer-tapping. Throughout compression, the tappet may not come into contact with the sample ring as further strokes will be directed into the ceramic plate, potentially causing it to shatter while abraded metal could contaminate the sample. 9. Stop tapping when the powder cannot be compressed further, so that the marked position on the tappet can be seen at the upper end of the funnel now. 10. Unscrew the funnel and adjust the cover plate into the sample ring. 11. Carefully unscrew the fixing screws from the cylinder. 12.