Prime Burning Off

[LiamPyro]

I've just got the hang of rolling stars and decided to make my first "big" batch, which is 350g (unprimed weight) of 5/16" Pihko Blue. Knowing that blues can be troublesome in terms of ignition, I primed them with 20% by weight (70g) of Fencepost prime followed by 10% by weight (35g) meal. Unfortunately, they failed the star gun test. I threw on some more Fencepost and meal and shot another star last night, only to find that the prime caught, appeared to almost burn out, and then the blue slowly ignited as the star was free-falling back to Earth. It's almost as if the prime just isn't creating the usual flame envelope that ignites the whole star smoothly and simultaneously. Is there any way to save the batch? Cutting a star in half reveals a visibly quite thin prime layer, maybe half a mil. Should I just add more prime? This seems counterintuitive, as the problem is in how the prime transfers the burn to the star... would adding more Fencepost prime help or am I better off just adding more meal? I hope this thread isn't redundant, I just haven't come across any posts about this exact problem. Any help is appreciated greatly!

[MadMat]

Try lighting a star that is simply laying on a flat surface. This way you can get a good look at what is going on. I have never rolled stars, but I do know a lot more solvent (water?) is used than in any of the other methods. I am wondering if this is causing your problems. Also, you could try test burning small samples of your fencepost prime and meal separately. This would eliminate the possibility that you made a mistake in making them (we all make mistakes from time to time!). I find the fact that you say your prime layer is very thin a little troubling as well. Though I only cut or pump my stars, I prime them in a pseudo-rolled manner. I take the fully dried stars and spray them with a dextrin-water mixture. I then roll them in a bowl with my prime material, adding more prime and spraying them with the water-dextrin mix as necessary. I call this a pseudo-rolled method, because it is done a lot drier than any rolling method I have ever seen done. I make sure to dry the first layer of prime completely before adding a second layer of meal. I always get a nice thick layer of prime with this method and it has worked very well, ignition-wise. Just a few thoughts.

Edited July 13, 2021 by MadMat

[Arthur]

Were the stars proven dry? A hard star comp can feel hard at 10% water content and it will not light. Weigh some stars say, 100g, then put them in a warm dry place for a day and re-weigh them, repeat til they have a constant weight.

[LiamPyro]

The stars have been stored in a ziploc bag with a small silica gel desiccant for a while, but you never know, maybe theyre not quite dry. Ill weigh them and pop them in the drying oven. The stars burn alright on the ground, although quite slowly. They seem to ignite better this way. Im not sure how fast of a composition Pihko Blue is supposed to be, but now that Im thinking about it, the star I tested recently out of the star gun burned really slow. Maybe moisture could be the issue....

[Mumbles]

You already got some good advice on things to look into. An additional possibility is that the stars are having a hard time staying lit while flying through the air. Some blue stars have a surprisingly poor critical wind velocity. As in they are capable of blowing themselves out if they're traveling too fast. It's a side effect of wanting to keep the flame temperature down to maintain the best colors. The way around this is usually a thicker prime layer or use it as a core in the color changing star. The thicker prime or outer composition is less to get it lit as much as it is to allow it time to slow down a little more and stay lit better.

[LiamPyro]

Yeah Ive heard about this issue with blues, although it seems that once the stars light they burn pretty vigorously - its just that they dont light quickly and evenly like most stars. Fortunately, when the stars were still 1/8 or so I split the batch and have been rolling Tiger Tail onto the half batch I saved.

[Arthur]

Some hotter primes bizarrely burn slower and with slag. Assuming your star is sulphur compatible, try a prime made of BP and unmilled BP ingredients and some silicon (metal) the BP takes and sustains fire, the ingredients slow the burn a little and the silicon burns to a liquid silica slag which is very hot and sticky and transfers heat well to the star.

 

But still a damp star will never properly light.

[LiamPyro]

Thats essentially what I used (Fencepost prime). Would adding more hot prime on top of the already BP-finished stars do any good? Would the slag stick around and help light the star even with BP underneath?

[deepakpyro]

Thats essentially what I used (Fencepost prime). Would adding more hot prime on top of the already BP-finished stars do any good? Would the slag stick around and help light the star even with BP underneath?

From my personal experience, i would say No. I used hot prime BP+si+mgal. Where i made mistake of adding less Mgal which doesn't turn Si into slag. So stars burned blind in shell due to hard break also and in star mine 60% of star lighten properly. I have tried to coat some excess layer of prime over the same star but again it was buring good in surface, 50% good in starmine and no luck in shell. But if you don't want to make the stars waste, prime one more layer and try soft break shell like waterfall effect.

 

Please note, my star had two layer of coating. Hot prime is 1mm and Green BP for another 2 mm. So this scenario may change in your case. Better try some sample

Edited July 15, 2021 by deepakpyro

[LiamPyro]

Well thanks for all the replies! I will make sure the stars are dry then roll some more prime on a few of them and see what happens. If they still dont light, maybe Ill try rolling the rest of the batch into bigger stars with a streamer composition. Its a learning experience for sure! Edited August 2, 2021 by LiamPyro