Prime

From PyroGuide

Prime and Priming

In Firework manufacture a prime is used to ensure the ignition of a star, a fuse, or any other situation where the desired composition is not sufficiently ignitable on its own for the given purpose. Usually priming involves the application of an easily ignited, but sufficiently hot burning composition with binder over the surface of the composition to be ignited. However there are some examples when priming is done in a different way, notably cross matching fuses.

The type of composition needed for priming varies considerably depending on the composition to be ignited. Black powder type compositions, Glitter compositions and Chlorate compositions may not need a prime, and if they do a layer of meal powder for the nitrate based compositions, and for the chlorate compositions sulfurless black powder or H3 will most likely be sufficient. For harder to light compositions, such as ones containing perchlorates or a large percentage of medium or coarse Aluminium, a hotter burning prime may be required. This can be achieved by adding metals such as Aluminium, Magnalium or Silicon to increase the burning temperature and in the case of silicon produce molten droplets of Silicon dioxide which stick to the composition increasing the time that they are exposed to the heat, and therefore the chances of a reliable ignition.

Step Priming

Some compositions may require a prime that burns at such a high temperature that it is hard to find a composition that reliably ignites it and it its self easily ignited. In this case two or more primes are used, each being harder to light but hotter burning than the previous one.

An alternative method using only two compositions is to coat the composition in a mixture of it and the final prime, then the final prime. For example: Potassium perchlorate red → 50/50 Perchlorate red/Meal → Meal.

Some stars may require more steps to ignite reliably. For example: Barium nitrate silver → 75/25 Barium nitrate silver/BP → 50/50 Barium nitrate silver/BP → 25/75 Barium nitrate silver/BP → BP.

Specific issues with priming, and special primes

When priming stars, especially ones which will be in shells with a particularly hard break, it should be noted that they may need a hotter prime than if the composition was in a device such as a gerb or a lance. This is because at high speeds friction with the air can make some compositions reluctant to take fire.

When colour changing stars are utilized a changing relay composition is used to separate the two layers. This is to prevent the slight differences in star sizes from resulting in both colours being in the sky at one time, and making the change look less uniform. Changing relay compositions are designed to have a minimum light output.

Another case where a special prime is used to separate two components which are incompatible. This buffer prime is commonly used to separate layers containing Potassium nitrate and some other nitrates from Ammonium pechlorate. This is usually a Potassium perchlorate composition bound with Nitrocellulose. The nitrocellulose is effective in preventing ion leeching between the layers. For a buffer between Chlorates and sulfur a base can be added to destroy acid, with or without nitrocellulose to prevent leeching. However it is recommended that alternatives are used where sulfur or chlorate are avoided. Ammonium compounds and Chlorates should never be used together, and due to the severe danger of the incompatibility. Buffering layers are not sufficient in this case.

Because of the incompatibility between Chlorate and Sulfur, Chlorate based primes are commonly used as an easier and safer alternative than using a buffer prime between the chlorate composition and a Black powder prime. The H3 burst composition or similar is a common choice. Also used commonly is Sulfurless Black Powder.

There are also alternatives to using buffering layers between between Ammonium perchlorate and Nitrates. These usually are in the form of Potassium perchlorate compositions, often catalyzed by Potassium dichromate, Manganese dioxide or other perchlorate catalysts to aid in ignition. Sodium nitrate does not have the same issues with Potassium nitrate, and can be used in climates where it's hygroscopicity is not an issue.

Red thermit, a combination of Red Lead and Silicon or Ferrosilicon is a special prime used to ignite compositions which are very hard to ignite, or where little or no gas is required.