Particle Size GuidelinesEdit
The subjects of this page are the following:
1.)"Commercial particle size specifications": Reading a pyrotechnic formula some of you may have wondered, if there are any special specifications for the particle size of chemicals, of which generally no mesh values are given. For example many formulas employ potassium perchlorate as the oxidizer, but a specific value for the desired particle size of this material is omitted. This is the case with many other reagents in many different formulas, which means that the pyrotechnician is not explicitly provided with the correct particle sizes for every of the compositon´s ingredients. Some of you may argue that any chemical´s particle size should be as fine as possible in any case, unless specifications are given. But this is not always true and sometimes makes the critical difference in the effect´s performance. The reason, why specific informations about the desired mesh size of many chemicals are generally omitted in formulas, isn´t because there are none. It is because there are general mesh specifications for different commercial raw materials on the market. Suppliers are used to sell their materials in a specific particle size, while the fireworks industry expects the reagents to come in this specific condition.
E.g. the commercial standard for potassium perchlorate is +170 mesh. This means that if a commercial composition employs potassium perchlorate as the oxidizer, this reagent is already this fine when getting incorporated into the mix, even if no formula articulates this standards. This becomes important when we prepare the same mix at home: We may have looked at our perchlorate, we may have prepared it and therefore say "this is a fine stuff". But who knows how fine it really is? It may be +60 mesh, which is quite fine, or +100 mesh for the most part. Generally it´s hard to tell by watching it. It may also be +300 mesh, thus being much finer than the stuff the pros use. These differences do not become apparent during mixing operation, where we generally use quite coarse mixing screens of about 20-40 mesh: each of the three listed perchlorate grades will pass the mesh and spread well into the mixture. But the performance of the finished composition will vary noticably (and this may be a reason why many homemade mixtures do not reach commercial performance). Therefore I call this specifications "performance-critical".
Thus, to avoid damaging performance the amateur will generally conform to the commercial specifications and will, if necessary, adaquately prepare his raw materials before every mixing operation to reach his composition´s intended performance. In this special case this means that we would presieve our perchlorate to pass 170 mesh before taking it to the real mixing operation.
2.) "Mesh-size-limitations for specific effects": This is not as critical as the former (because we generally recognize it). It means that there are practical limitations of a chemical´s mesh size, within which a desired effect is obtained when we use the chemical in an appropriate composition. We generally know that e.g. a waterfall effect "requires" coarse aluminium flake (flitter) and therefore will not work properly with only bright alu or even only atomized alu. In this manner, we also know that a bushy charcoal comet will "require" a special type of charcoal (e.g. pine) coming in a special mesh size. Such "effect-critical" specifications are generally explicitly presented in a pyrotechnical formula, therefore there is only little danger of ignoring them. E.g. if Lancaster lists 350+ mesh atomized alu as an ingredient of a glitter composition, the effect will generally fail or suffer hard if we use coarse grades.
The following list presents commercial mesh specifications for different chemicals I extracted from pertinent literature by Lancaster(L) and Shimizu (S). The authors somewhat differ in their specs given. On the right hand some general mesh-guidelines for use in specific effects are given. For many chemicals the authors didn´t specify mesh standards. Feel free to expand the list, if you have access to missing specs given by other reliable sources. Note that e.g. +120 means that 100% of the chemical pass 120 mesh. (Admiral)
|Reagent||Commercial Standard (mesh)||Limitations for desired purpose (mesh)|
|Ammonium perchlorate||120 (L); 90% +80, 36% +270 (S)|
|Realgar (Arsenic disulfide)||+80 for smoke, +140 for report (S)|
|Copal gum||60-200 (L)|
|Charcoal||Airfloat for gunpowder, fast effects; 40-80 or 30-40 for slower effects (L); Pine comes +300|
|Potassium benzoate||Dry +120 for whistle mix (L)|
|Magnalium||30-50 for crackling, +120 for strobes and other stars (L)|
|Magnesium||Coated 60 for colored stars (S)|
|Sodium oxalate||120-200 (L)|
|Sodium salicylate||+120 for whistle mix (L)|
|PVC||0.2-2µ milk or 20-150µ grain polymerized (S)|
|Red gum (Accroides resin)||30-80 for illumination, +120 in stars (L)|
|Sulfur||+120 (L), +70 (S)|
|Strontium carbonate||120-200 (L)|
|Strontium nitrate||+80 (S)|