In places where good quality black powder was made, the powder was examined immediately after the blending process was completed. They would also periodically take small samples from powder stored in warehouses for analysis, to make sure that it was still usable.
The first thing they would do is give it a visual inspection. The color of good quality black powder should be a uniform dark gray (or slate) color. If the color has a blue tint or is very black, then this indicates that the powder has too much charcoal or contains too much moisture. Powders made of red charcoal (such as cocoa powder) should be of brownish-black color.
A sample of good quality black powder. Click on the image to enlarge.
After this, they would examine a small sample with their eyes or through a magnifying glass. Properly mixed powder should not show any difference in color even when crushed, nor should it be possible to feel sharp particles. A variety of colors indicates that the powder was not mixed evenly and the presence of sharp particles indicates that the ingredients were not pulverized properly. Bright or bluish-white spots in the powder indicate that the saltpeter has effloresced during the drying process, which will also affect the properties of the mixture.
The powder would then be allowed to run over a sheet of paper and the paper would be examined. Properly made powder should not transfer its color to the paper. If this happens, this indicates that the powder has too much moisture or dust (meal powder).
For prismatic powders, they would check to see if the prisms have smooth surfaces and the edges are sharp and complete. They would also check to make sure that the prisms don't easily crumble or give off too much color when rubbed against a sheet of paper.
The next thing to check was the solidity of the grains of powder. Good quality powder grains should not be easily crushed by finger pressure. It should not fall into dust at once, but should break up into angular splinters. In Germany, they would put 1.1 lbs of powder in a leather bag, which was then put in a glazing drum and rotated for 15 minutes at 15 revolutions per minute. After this, they would take it out and weigh it again and the loss of weight should not be more than 1.55%. In France, they would take an average of various powder samples and dust it initially and then take 8 kg. (17.6 lbs.) of powder and put it in a barrel designed to hold 12 kg. (26.4 lbs.) of powder, which means about 1/3 of the barrel is empty space. This barrel would then be enclosed inside a second barrel and then rolled down an incline of 15 degrees for a length of 5 meters (16.4 feet). The incline was made of planks and at the bottom was a bale of hay to stop the barrel. At the side was another incline made the same way, but falling in the opposite direction. The barrel was allowed to roll down one incline, then sent back down the other incline and the process was repeated 100 times, so that the barrel would have traveled a total of 1000 meters (3300 feet). The powder was then dusted again and the remaining grains were weighed. If the powder did not lose more than 0.20% weight after this test, then it was deemed to be of good quality.
The next process was to examine the size of the grains. They would do this by taking a sample of powder (typically about 2 kg. (4.4 lbs.)) and placing it in a frame with a number of sieves in it and a tray at the bottom. The sieves would have meshes with different sized holes, with the sieve with the largest holes at the top and the sieve with the smallest holes at the bottom. They would place the powder sample on the top sieve and then shake the entire frame for a prescribed amount of time (which depended upon country) and then see how much of the powder sample was held in each sieve. There were quality standards defined for how much each sieve could hold, depending on the powder type. For instance, for good quality rifle powder, no powder must be retained in the first sieve, less than 5% in the second sieve, up to 65% in the third sieve, up to 50% in the fourth sieve and 8% at most in the fifth sieve. Similarly, for good quality cannon powder, no powder must be retained in the first sieve, not more than 5% in the second sieve and no more than 10% in the fifth sieve and all the remaining should be in the third or fourth sieve.
In France, they would additionally also count the number of grains in a gram of powder sample to check if they were within certain limits depending on the type of powder.
In our next article, we will study some more physical properties they would study to ensure black powder quality.