18 replies to this topic

[Strobe]

Hi,

I'm planning on trying out my 1st star comp today. The formula is from Intro to Practical Pyrotechnics:

Blesser Purple
KP - 68
cupric(II) oxide -9
Strontium Carbonate - 6
PVC - 11
Dextrin - 5
Solvent - Water/25% alcohol

I weighed and screened the dry chems (100g total) together yesterday and will attempt to make cut stars this afternoon.

Can anyone give me a rule of thumb regarding how much comp to reserve for priming? I gather I should keep a little extra on hand in case I add too much solvent as well.

Should I anticipate any difficulties with this formulae and cut stars? I have a couple of plastic syringes I could use to pump them if needed. I stayed away from the red gum formulas as I gather they can be pretty sticky and difficult to work with.

[Creepin_pyro]

I've cut these stars in the past with no problems. They make a very nice purple.

I'd say reserve 10% comp incase you over-wet. Should suffice unless you go crazy with the solvent!

Not sure on the ratio of prime to comp - I've never heard of a rule of thumb for this. What are you planning to prime them with?

[Strobe]

I had thought to prime with a graduated mixture of BP and comp. Do you think that would work with this type of forumla or is there something else that would work out better? They will be cut stars so there will be square edges but I'm not sure how hard this will be to light given the KP componant of the formula.

[Creepin_pyro]

I'd try them with straight green meal first. From what I recall, they are quite easy to light and to not require a step prime, especially with cut stars. It couldn't hurt though...

Adding Silicon or Aluminium powder also helps to increase the efficiency of a meal prime.

[karlfoxman]

I used this formula in a 6" shell of shells, the shell had a 1 3/4" blesser kp purple comet on top too! Very nice colour, I changed the strontium carb to 9 parts and used parlon not pvc. Ill get a vid of it on here. My stars and comet were primed with milled bp and all lit.

[Strobe]

Yes, Please post your video Karlfoxman, I'd love to see it.

I think things turned out pretty well for my 1st attempt at stars. I'm not sure if I got the moisture content completely correct for the solvent (used 25% isopropyl in water). I could never get the comp to a dough like consistancy, it came out with more of a sandy mud texture. I kept adding solvent until I could compress the comp into a hard ball and break it apart with a finger with only a few large pieces forming vs a lot of small ones. No moisture came to the surface when compressed so I'm guessing I didn't use too much solvent.

When I did the cutting, the cubes mostly stayed together but did deform a decent amount in the process of separating them and coating with a little dry comp. I burned a few after about 5 hours of drying and they lit easily enough with a torch lighter, burned completely and had a nice color.

If done correctly, how hard should they come out when dry? I could crumble a star between my fingers with moderate pressure after about 5 hours drying time, but I'm not sure how long they'll need to completely dry.

[Creepin_pyro]

They should be too hard to break between your fingers once fully dry (or at least VERY difficult to break). What kind of conditions are they drying in (temp/humidity/wind?) I usually leave my stars to dry for at least a few days, depending on solvent used/star size.

[Strobe]

They're drying in a shed so there is no wind. I may take them out this afternoon if we get some sun. temps are in the 60-70 deg F range during the day but there was some light rain yesterday so humidity might be an issue.

I'll try crushing another this afternoon between my fingers to see if there is any change in hardness. If they turn out too soft I can use them in a mine or fountain at least?

I guess I need to make a star gun to test them out with next. How long of a tube would I need and what sort of lift charge would I need to use? The stars range from around 1/4 -3/8's inch in size. I have some commercial FFg BP and some homemade BP that was made via the CIA method available.

The homemade stuff is was done with hardwood airfloat and I have not milled it yet. I just pressed it through a 20 mesh screen after queezing out the moisture. It seems to burn well but I have not tested the speed so far.

[BrightStar]

Strobe, it sounds like your stars will need another couple of days drying. Dextrin bound cut stars can be a bit crumbly, but when properly dry mine tend to snap sharply when broken by hand.

Don't worry about using them in a shell - the worst that can happen is that the larger ones might shatter into smaller pieces; as you have a range of star sizes anyway and it's a fairly easily ignited comp it should look OK.

As for the star gun, I improvised one a couple of days ago using a cardboard 1lb rocket tube (0.75" id x 7.5" length), bentonite base plug, small fuse hole, 1/2 teaspoonful of BP with the star on top, then some crumpled tissue lightly consolidated to give some back pressure even if the star is smaller than the tube.

It's hugely satisfying to see a newly dried star burning as it sails above the rooftops

Edited by BrightStar, 20 April 2007 - 09:33 PM.

[Strobe]

I had a chance to test my stars this weekend at the beach. They turned out to be quite hard once completely dry by the way.

I didn't have a tube close enough in diameter to the star sizes, so I decided to try using some in a mine. This was my 1st attempt at a mine as well. Unfortunately they ended up blowing blind. I'm not sure if did something wrong with the mine or that these really do need priming.

For the mine, I used a 1 inch ID tube, poured 7 grams of commercial FFg powder in the bottom, lightly tapped in some tissue paper on top of the BP and then put the stars on top of the tissue paper, followed by another layer of tissue paper. Any chance somethng about the way I made the mine would have interfered with the stars igniting?

[portfire]

Hi strobe.I would say it was the tissue paper.If you have any stars left,try using a tight fitting disc with holes in to passfire.

[maxman]

You might have put a bit too much lift in there and blown the stars out.
I dont usually put paper on the lift, I just put 3g or so lift then stars and then a stiff cardboard disc on top.

[Creepin_pyro]

7g lift for a 1" mine is an awful lot - I'd start with around 2g and go from there. Remove the tissue above the lift and replace it with either nothing or a paper disc with holes in. For such a small mine I don't think there's much point in using the piston method. Dribbling a little loose meal inbetween the stars can also help with ignition.

[BrightStar]

I'm quite surprised that Bleser Purple relies on the dextrin and PVC alone as fuels... I would have expected some Red Gum or other resin in there.

Apparently it must work though... I wonder how the choice of fuel affects the ignition characteristics?

Edited by BrightStar, 26 April 2007 - 05:10 PM.

[Strobe]

I can give the tight fitting disk thing a try. What function does that disk have, is it to build pressure or something?

I took a guess at the lift charge amount based on the mine instructions from Intro to Practical Pyrotechnics. Unfortunately they called for a 2 inch I.D. tube and 10 - 17g of lift (if I remember correctly), so I figured 7g might be ok with a 1 inch tube (didnt have 2 inch tubes around either). I'm not sure if this is important, but I drilled a hole in the bottom of the tube just above the clay plug and used that hole for the fuse.