Now and then on the pyro discussion lists someone will bring up the subject of zinc stars. Usually several folks will chime in with, “Oh, man, those stars are some of my favorites, so subtle and beautiful.”
In Chapter 15 on Fireworks, of Alexander Hardt’s Pyrotechnics, (this chapter written by Barry Bush after Dr. Hardt’s death), it is stated, “Good zinc stars are blue-green with tails of delicate gold, and seem rather exotic today.”
This is a color star where the color is produced by an elemental metal, rather than a metallic salt, such as when a blue is produced with a copper oxide or carbonate. So, this blue-green color star may be among the oldest firework star colors that were produced.
Back in the early 90′s when I first started making stars, there was not much fireworking information available. I was able to get my hands on a copy of the then recently reprinted Pyrotechnics, by George Weingart. Some of my first star-making efforts were based on a few of the formulae contained in that book, and perhaps my favorite of them was the Granite Star.
An added bonus is that this is one of the easiest cut stars to make that I’ve tried.
(The percentages, because of number rounding, actually add up to 101%, but that’s OK, and they’ll work just fine. The percentages of each individual chemical in the star composition are calculated by taking the original number of parts of that chemical, say 14 parts of KNO3, and dividing that number by the total number of parts, 64.5 in this case. 14/64.5=.217, which can be rounded to .22, which is 22 hundredths or 22%.)
Note: You may be saying to yourself, “I wonder why he’s including those decimal numbers after the percentage numbers.” I’ll show ya in a minute. The decimals are much more useful than the percentages.
Harry Gilliam, in the last blog post, published the formulae that he inherited from the Kosankes when he purchased the business that became Skylighter. In that list of formulae is one called Pearl, and it is a slightly different version of a zinc star:
I always like to look at star formulae and see how they differ from each other. It can be seen that the second formula uses less zinc powder, more KNO3, and slightly more charcoal, sulfur and dextrin.
There is a formula in Hardt’s book that is similar to the Kosanke formula above, but the zinc is increased to 45%, and some Meal D black powder is used in it, as well as potassium nitrate, charcoal and dextrin.
I, personally, have only made zinc stars using the first formula, from Weingart, the Granite Star.
In a recent discussion in the Passfire.com Forum, a fellow fireworker, who has worked quite a bit with this star, recommended that the charcoal used in the formula be half airfloat and half 80 mesh. This improves the charcoal tail that the star leaves behind as it burns. Back in the ’90′s when I made the star, I’d only use airfloat, so this is another area of experimentation as an individual fine tunes the formula to his own personal tastes.
These stars light easily, especially when made as cut stars with all the corners and edges to take and hold fire, so I’ve always just primed them with a “scratch-mixed” (mixed by hand, no milling) black powder prime, simply screened through a 40 mesh screen.
|Potassium Nitrate||75 OR 15||75%||(0.75)|
|Airfloat charcoal||15 OR 3||15%||(0.15)|
|Sulfur||10 OR 2||10%||(0.10)|
|Dextrin||5 OR 1||+5%||(0.05)|
|Totals||105 OR 21||105%||(1.05)|
Note: This is simply 75/15/10, KNO3/charcoal/sulfur (the classic black powder proportions), with an additional 5 parts of dextrin added as a binder (additional 5%). One of the few formulae that I can always remember off the top of my head is the 15/3/2/1 parts proportion of this composition. If I want to make 21 ounces of prime, I simply weigh out 15/3/2/1 ounces of each chemical and screen them together.