Here are two photos I just took. They are digital, forgive that. They merely underscore a point for Analog photographers.
The first, on the left shows 3 mounds of Sodium Chloride. The one on the left is a white powder and is Analytical Grade, the one in the middle is Technical Grade and is lumpy. The one on the right is pure white and consists of pure cubes. It is food grade table salt.
The one on the left is suitable for emulsions or processing solutions. The one in the middle works in most processing applications but cannot be used in emulsion making due to aggregation and fog. The one on the right contains Iodide salts (in various states as pure NaI is unstable) and it contains silicates. It cannot be used in either processing or emusion making. Appearnce wise the one on the right appears to be the best, but it is not.
Now, the second picture shows two mounds of salts, KBr (Potassium Bromide) and both are analytical grade. One, on the right, is a powder and the other consists of cubes. The cubes cannot be measured by teaspoon due to their shape and the difficulty forming an full teaspoon evenly, so I used the small cup in the background.
That cup will contain 17.2 grams of KBr in cubic form but will contain 20.4 grams of the powder. This is the type of error to expect when measuring out solids using spoons.
I test my premises about accuracy and purity by actually running tests.