One of my favorite powdered blends comes from San Francisco's Sword and the Rose
that can be piled and shaped and lit and it smokes very well. I just got a batch when on a recent excursion to the Bay area and spoke to the maker but not begging any secrets from him. He did say there was some salt peter in the ingredients.

When making my own incenses, Ive never been one to use salt peter although Im not fearful that it is toxic or unmagikal. I prefer to make pellets (as did the Egyptians) rather than cones or sticks or having to use coals.

Nor do I tend to measure and maintain ratios as Ive found the ingredients often provide their own clues as what to add. And I must confess the concept of self-ignition scares me as someone who works with the fire element but thats probably my own linguistical hang-up

That being said . . .

Ive found that substances like Camphor (powdered finely and blended well) can create a continuous burning effect ie. smoldering.

Other additives Ive found helpful in this regard are ground Charcoal (preferably from a witchie sourse like a lightning strike or the remains of the maypole from last year) and also Pinon infused wood.

Pinon is my mainstay as a base as they are abundant here in the high desert. Although Pinon can be trickier to work with as it can be found in a wider range of consistencies each with properties that are useful in balancing out any particular batch - some more on the wood side of the spectrun and some more pure resin. The straight up sap (ie resin that beads on the trees) has different properties than wood (collected from fallen trees revealing the inside matter) some of which infused with resins due to wounds, bugs or rot. This more woody type I have found powders well, is less sticky when grinding and sifting and allows for a continuous burn with phenol type smell to the smoke.

But the camphor and the charcoal seem to work well in achieving a continuous smoldering effect.

angel food for thought,

HITIRUS

Wylundts Book of Incense has some great recipes to make self burning incense, stick and cone incense, and scented briquets.