The one question we are always being asked is what is the grit rating of our polishing bars and pastes?
Attributing a grit rating to a grain size can be very misleading, as the grain size has no bearing on the hardness of the grain itself. A good example of this is bolpol DG Tripoli Powder in Cream and Rose; both these powders have the same range of grain sizes, but the Rose Tripoli has a harder grain than the Cream and, therefore, has a more aggressive cutting action. Different abrasive powders also break down in different ways, with some maintaining a sharp cutting edge while others become more rounded
To give a more accurate guide to how the compounds perform they are each graded with numbers from 1 – 10, with each bolpol bar having two numbers divided by a /. The first number is how abrasive the compound is (the higher this number the more aggressive the powders within the bars are) and the second number indicates how much colour (shine) the compound will give (the higher this number the more colour the finished piece will have). By comparing two very different bars you will see how the abrasives within the bar impact on the polishing process.
Example one – Grey polishing compound 8/10 for cut. A 1st stage polishing compound for use on iron and steel.
Example two – Brown Tripoli compound 7/10 for cut. A 1st stage polishing compound for use on soft metals (like brass and copper) and hard plastics.
Both these compounds are designed to remove grinding, tooling and casting marks and, based on grain size, both these bars may have a similar grit rating. The grey compound, however, contains harder abrasives and using this on a soft metal will do more damage than good. The Tripoli bar, which has a softer abrasive, will have a lesser effect on hard metals.
The carrier for the powders is a mixture of waxes and binders, with added colour for ease of identification, and has little to no effect on the abrasive properties of the compound. The colours used in bolpol compounds broadly reflect the industry standards when matching a colour to the material being polished.