From PyroGuide Edit
Portfires are used to light fireworks pieces and usually burn three to four minutes. They drop hot burning dross unless a more expensive color mix is used. The following is a redesign of a mix presented by Lancaster (Fireworks Pr. and Practice). It is very cheap, easily made, and gives good results.
This is charged by funnel and wire, or simply hand-pressed, into a container made of kraft paper. The container is made simply by forming around 9-10mm dowel, 4 layers thick. It is dry-wrapped, and only glued on the outside layer. The tube should not be thicker than 3-4 layers because it has to burn away with the composition. Dry it on the dowel to prevent the tube from bending into one direction. The 38cm size is typical and burns about four minutes. Other sizes can be used but portfires over 38cm are not commonly used due to their size. Remember not to use to much pressure when loading. It is enough to move the drift up and down by hand-pressure until the charged increment is consolidated. Do not use a mallet. You can either charge the whole tube with composition (which means it has to be thrown away when reaching the hand) or charge the first 10cm with clay, or alternatively, a wooden stick of the desired bore and 10cm in length can be glued in place. The latter methods mean that the fire stops when only 10cm of the portfire are left. The upper end of the portfire is primed with a gunpowder slurry, or a piece of black match can be embedded.
For portfires it is not desirable to perfectly mix the components since a slow burning speed is required. Therefore the three components are brought together with mortar and pestle until the rather coarse mix has a uniform yellowish-green colour. The ingredients shall not be ground in a mill before mixing, so e.g. the sulphur can be full of lumps. It is possible to use cheaper, technical-grade sulphur in portfire compositions, as there are no cholrates in the mix. The black powder used can be a simple mortar and pestle mix and a high-grade powder isn't necessary or recommended because it is only included to keep the portfire burning. Mealed gunpowder burns too fast and should not be employed at all. The dross produced can be reduced by minimally increasing the percent of charcoal used, but this has disadvantage of allowing the portfire to be more easily extinguished. Well-made portfires are quite resilient, and should stay lit, even when dropped onto their burning end from 50 cm.
More formulas for portfires. Lancaster C is a colour mix.
Sources: Lancaster, Ronald: Fireworks. Principles and Practice, 3rd edition, p. 226f Retrieved from "http://www.pyroguide.com/index.php?title=Portfire