Glitters are rather uncommon but very beautiful and safe pyrotechnic effects. Unfortunately they require some special knowlegde to be made successfully: They require special mixing methods to give the best possible effect, special care when making them into stars and they do require safety precautions. What is true with common stars often isnÂ´t with glitters.
The chemical contents are imaginably simple: there are the processed or unprocessed gunpowder ingredients, there are metal powders and there often are additional oxidizers or other agents such as bicarbonates. But the glitter thing isnÂ´t that easy.
Maybe the best sources on glitter are Dr. WinokurÂ´s Pyrotechnica articles and OglesbyÂ´s highly theoretical work about itÂ´s "Chemistry and Techniques". Both are a highly recommended read. This page tries to summarize some of the two sourcesÂ´ most practically relevant findings in checklist style.
- Glitter mixes often call for finely divided aluminum. Unless specifically stated otherwise fine atomized grades are used for this purpose (often -325 mesh). Many older formulas make use of "bright" grades and these can provide superior results as well. When magnalium is used, particle size specs are often explicitly given.
- Avoid ball-milling glitter compositions! Many experienced pyrotechnicians have pointed out that ball milling can have a detrimental impact on the performance and appearance of glitter stars, a fact that is mentioned even by Ronald Lancaster. Glitter compositions are best hand mixed by the use of screens, preferably coarse in mesh size. Lancaster votes for 18 mesh. Even if ball-milling was ever used to integrate glitter mixes, we must leave out any metal powder from the mill at all costs! In this case the metal would be mixed in by hand after the milling process is complete.
- The kind of charcoal used is important to manipulate the effect inasmuch as fast reacting charcoals (such as willow) give us more of these droplets ("Spritzels") with less delay (they maybe make a "bushier" comet) while hardwood charcoals result in larger spritzels with less delay. Relatively short-lived glitters with a small tail are often called "Pearl".
- To achieve longer tailed glitters of special beauty (often referred to as "Tremolante" and "Twinkler") we must make use of coarse additives e.g. charcoal, magnalium or aluminum flitters. By adding a few percent of these materials, the tail is lengthened because the coarse particles act as cores for the formation of large and slow-reacting droplets. Carbonates (of barium, strontium, sometimes of lithium as well) and bicarbonates (of sodium) also retard the effect and are popular "delay agents" in many mixes. Where not present by default, a few percent can be added to tune the effect.
- Glitter is a complex phenomenon contingent on many factors. There are numerous other properties of chemicals, particles etc. that affect performance. For improved effect and combined glitter mechanisms (combining different glitter colours and types e.g. to make a yellow or even pink pearl-headed effect with a white twinkler tail) special mixing methods such as ricing and wet blending are used. Here the reader is referred to L.S. Oglesby.
Wetting and storing Glitters:
- The excessive use of water during consolidation can ruin a glitter effect. All present materials form saturated, often basic solutions with water and damage the metal fuels. The longer the composition is wet, the more likely the metal fuels are to be damaged. Thus we must use the minimum amount of water practically employable. Oglesby states that "unless the mixture is to be granulated, the water used for forming the material into stars should be no more than the weight of the charcoal used in the mix." This means that a e.g. kilogram batch of a comp containing ten percent total charcoal is wetted with no more than 100g of water. Consolidating a glitter mix really is different: there will be much less water you think itÂ´s gonna be, and the mix doesnÂ´t even look wet.
- Oglesby denominates the two most important factors in metal corrosion in wet mixes as pH and temperature. Boric acid is often added to balance the pH of alkali glitter mixes and to prevent the aluminum from being corroded. Although common practice, it is a bad idea to add boric acid in powdered form (in so called: add.%) because (also due to reduced water content and weak solubility of boric acid: about 5g/100ml of water) a small amount of acid never succeeds to be adequately spread into the mixture and to protect the metal.
- To sum this up, the author found that using 10% by weight of 2% boric acid solution in water with additional 5% alcohol works well for most aluminum glitters and does not damage the mix. Work quickly as such a small amount of water evaporates very fast. The two percent of boric acid are easily soluble in water and the alcohol helps wetting the charcoal. Using an acidic solution instead of solids ensures that all the metal is well protected. When magnalium is employed as the metal fuel, the same solvent is used without the boric acid, which corrodes magnalium. Some people argue they successfully used boric acid also in the latter case, but this is not recommended. If any magnalium protection is necessary at all, we would much rather turn to potassium bichromate. However, some pyros like Perigrin suggest the use of an enormous 33% alc. in water to dampen glitters, but with only about 5 grams of water per 100g of comp, you will have to work quite fast...
- Against this background glitter compositions are best made into pumped stars. The higher amount of moisture necessary for cutting will most likely damage the performance of the finished stars.
- The second problem we have to deal with is temperature. High temperatures promote chemical reactions and a warm but still damp glitter star will invariably lose metal fuels. Thus, it is very unwise to proceed as usual and dry glitter stars in the sun. The mix should stay cool during and after manufacture until dry. Oglesby suggests to make glitters during the winter months.
- Finished stars should be thoroughly dried and stored in moistureproof containers, for obvious reasons.
- Although glitters are among the safest fireworks mixtures it is necessary to protect ourselves with the usual equipment (gloves, mask etc.). Many glitters contain toxic compounds such as barium salts or antimony sulfide.
- Note that glitters often contain comparably high amounts of sulphur or sulphides (e.g. of antimony). The compositions must not be used in combination with chlorates or phosphorus!
- When glitter stars are intended to be used in aerial shells (or other devices shot at a considerable distance) Oglesby recommends using compositions showing an aluminum content higher than xx percent; otherwise the effect tends to look too dim when viewed at a distance. It has to be remembered that the aluminum is what makes the main effect.
Sources: Oglesby, Lloyd Scott: Glitter. Chemistry and Techniques