As stated previously, the precision scale recently bought was instrumental in creating a test board, with 8 patches of earth formula. This is simply a 1-cm thick foam board, on top of which one sheet of plaster cloth was applied - both to provide better grip for the zip texturing to come, and to replicate exactly the layout structure. The starting formula was the now classic 5 parts plaster, 1/5 parts burnt sienna dry pigment, 4/5 orange dry pigment. Each patch has a known ratio of blue ultramarine pigment, which was increased in small doses against each one. For each patch, the procedure was similar - wet the spot with white glue, apply the corresponding formula with a tea strainer, leave to dry for 1 hour, then repeat again in the same location, then move on.
After adding the determined weight of blue ultramarine dry pigment - usually around 0.04 grams - the whole formula would be thoroughly mixed in a "shaker" for 4 minutes, as to ensure a uniform outcome (the days when I would use a spoon to mix things are long since gone - since applying the resulting mix resulted in particles of the stronger pigment - then black - "shining" through the whole formula).
As the last patch on the first test board was still not matching the medium earth color on the layout, I decided to extend the batch of tests on another test board. Photos 2 and 3 show the first test board and second one, respectively. The white spots on the edges of the patches represent white glue, migrating from the patch under work to the previous one(s), already finished. Not a big drawback since the colors can be matched like this with no problem. The 2nd board still needs to have one application over the 7th patch, and the last one completed.
For both boards, the order of the patches if left to right on the top row, then right to left on the bottom row - so that the 1st one is on top left, while the 8th one always on the bottom left.
The percentages of blue ultramarine dry pigment is as follows: 1st test board - patch 1: 0%, patch 2: 0.1%, patch 3: 0.22%, patch 4: 0.43%, patch 5: 0.61%, patch 6: 0.9%, patch 7: 1.2%, patch 8: 1.6%. 2nd test board -patch 1: 1.8%, patch 2: 2.0%, patch 3: 2.2%, patch 4: 2.5%, patch 5: 2.8%, patch 6: 3.1%, patch 7: 3.3%, patch 8: 3.5% (patch 8 not visible in the photo at this time).
The last photo shows both boards alongside, just to get an idea of the color ranges in both.
