Deep blue/violet microstars

[optimus]

Ever since seeing a commercial fountain with these kind of microstars, recreating the effect has been high up on my pyro to-do list...

 

This formula looked very promising, but I don't have access to HCB. I tried it anyway, and as expected, it didn't work very well.

 

Chinese deep violet-blue microstars

Source: Myke Stanbridge / Rec.pyro

 

Potassium perchlorate to pass #240 39.0

Black copper oxide to pass #240 37.0

precipitated sulphur to pass #240 15.0

Hexachlorobenzene (HCB) to pass #60 6.5

Acacia gum, a top quality fine dust 2.5

 

I asked Crazy Swede for some advice, and thought some others here might be interested in some discussion on the subject. I think it would be greedy to keep such good advice to myself, so here it is:

 

"I’m afraid the volatility of HCB is what makes that Chinese composition so special. They burn slowly and leave a big amount of slag from each star. Since the non-gaseous combustion products end up in one solid piece of slag, the flame is very clear and the CuCl*-radiation is so pure that the colour looks violet blue instead of deep blue.

 

Many years ago, I tried hundreds of experimental blue compositions in an attempt to duplicate this particular effect. I did not have access to HCB and tried instead to evaluate different cool burning fuels and flame expanding additives like hexamine, guanidine nitrate and nitroguanidine.

 

I don't have my old note books at hand and I can't remember the best composition (I never succeeded in getting the perfect blue anyway!) but the copper source was CuO, the oxidizer was ammonium perchlorate and the main fuel was red gum. Nitrogen rich compounds were added in such amounts that the composition only smouldered. Then small amounts of fine magnesium powder were added to bring the burning speed and flame size back to reasonable levels. Ammonium dichromate was added in small amounts to inhibit the corrosion process between ammonium perchlorate and magnesium. They were bound with NC solution.

 

The result was a star that burned with a violet blue flame and left one piece of solid slag. When shot in a mine the stars looked a little dim and the flames were rather small.

 

Since I didn't have a big interest in using them as micro stars I gave up on those compositions and turned to more conventional ones since they looked better in the air, even though their colour purity were lower."

 

So, it looks like I won't be able to get the formula working properly without using HCB. Has anyone else tried making this comp without HCB?

 

I've also tried using Burdick's blue strobe comp made into microstars. They look great, but they're not a deep blue/violet - more of a purple/blue.

 

Ammonium Perchlorate 63

Silicon, GE II 22

Copper(II) Oxide, black 10

Polyvinyl Chloride (PVC). 5

 

I'm now considering trying to tweak this formula to get the best colour. Obviously it's for a strobe propellant, so it makes sense to me that it could be made to function better as a coloured microstar. Perhaps increasing the percentage of Copper Oxide?

 

If anyone has any advice for me, I would really appreciate it! I would be a very contented pyro if I could get these deep violet/blue microstar fountains working properly!

[cplmac]

I made some of the silicone II blue strobe mix, and it did not strobe at all. The blue was nice though. Something was different in the formula I made, I'm going to try and dig it up will let you know.

[Mumbles]

This isn't exactly on the same topic, but another common way to create micro stars is by using gerb compositions. If you found a purple that you really liked in a gerb, you could possibly make it into micro stars.

 

Back to said topic at hand. You may want to try Parlon in place of the HCB. In some situations in can be an acceptable replacement. It can be used in some organic strobes for instance. I've heard of some people using Hexachloroethane in place of HCB as well, but never heard how well it worked. I would think it might vaporize out of the comp before it could be properly utilized. Of anything Dechlorane is probably the best bet. I have heard first hand accounts of Dechlorane working well as an HCB substitute. Too much can cause a whitening of the flame. I think the HCB content is low enough to prevent that.

 

Anyway I have access to all the aformentioned chlorine donors, yes even the ellusive HCB. I might try them out. Use HCB as a control to see what kind of results I could get off of Dechlorane, Parlon, etc.

[Mumbles]

Not sure about china and such, but this is true for the maltese at least and some Amercian builders, as well as a few PGI members. They keep their formulas secret like it's the last sliver from Jesus' cross. In some cases you're lucky to even find out what the coloring agent is.

 

Most companies have year and years, sometimes generations to get their formulas just right. They all have their own formulas.

[cplmac]

Very True, getting an actual formula is near impossible unless you are a friend, and even then you aren't likely to get the whole truth. I have made about a dozen different comps right out of the book from Purrington and OFCA, and only once or twice have I gotten a formula that didn't need a tweaking to work right.

[Mumbles]

Some of the older members from the PGI will give you anything you ask for. Jim Freeman, and Steve LaDuke come to mind. Say Hi to them, and 3 hours later when your mouth is parched from taking and brain hurts from trying to take in everything, you're halfway to grandmaster as far as formulas, technique, and tricks.

 

They know they won't be around forever, and love the hobby and want it to last as long as possible. I have a similar outlook, even though I am tad bit younger. Anyone who has contacted me knows I don't stinge out on anything you ask. The only things I keep private is the stuff that I have recieved from others with the promise that it stays confidential.

[optimus]

Thanks for the input guys. I think I'm going to proceed by tinkering with the strobe formula and see how that goes. The Chinese formula looks like it's going to be harder for me to get to work properly, but if anyone feels like doing a few tests with it I'd appreciate hearing the results. Mumbles, I'd love to hear how different chlorine donors work if you do get some time...

 

I never really understood fully why one would keep formulas secret. I can't imagine having particularly good colours would give a pyro company any kind of commercial advantage - I doubt the average consumer would even notice! I can't think of any effects which are only produced by one manufacturer either.

 

I tried to encourage people to add to the shared section of the Passfire formula database on REC.PYRO, but the thread kinda went off on a tangent, as was to be expected!

 

I'll be sure to let y'all know how I get on with the tinkering, even it I stumble upon that elusive perfect blue

[Mumbles]

I have some time here before school starts again. I might give them a try. Any ideas how the best way to test would be? Fountain? comet? just alone on the ground?

[optimus]

Bugger.

 

I just noticed the special notes for the formula posted on rec.pyro:

 

"The use of Acacia gum is rather special for

not melting during its decomposition, where its hydrogen is

released as water vapour with a minimal effect on colour. I

naturally tried the various combinations with many chlorine

donors, including dechlorane, but it was not as good. Oddly

the formulation is very tight, and even tiny changes make a

very big difference in the final performance. Changing star

size to even 5 mm leads to a marked decrease in performance

over the 3 mm microstars."

 

Sounds like the tests have allready been done, and to do them again would be a waste of your time and chems... sorry about that - should've read up a little more

[Mumbles]

Quite alright. I might still try the HCB and a few other versions to see what the fuss is about.

[Crazy Swede]

...They keep their formulas secret like it's the last sliver from Jesus' cross...

 

...Most companies have year and years, sometimes generations to get their formulas just right...

Regarding formulas from books and the Internet that doesn't work as good as expected:

 

The secret is never in a formula!

 

It is always about knowing your chemiclas and continually adapting the techniques used to optimize the result. A formula is never static! For example, where I work, I have to change the formulation for smoke and illuminating compositions several times per year to compensate for differences in the raw materials.

 

I know people in the business who have spent years to adjust their formulas for ordinary colours. Still, if I tried their recipies with my materials, I'm sure the result wouldn't be anything special.

 

A formula should only be seen as a starting point and I believe that those who keep their formulas secret might not have understood this!

[Crazy Swede]

Regarding Optimus quest for microstars emitting pure CuCl radiation, Dr. Myke Stanbridge has a theory that it is hard (or even impossible) to create a good blue flame with materials containing too much hydrogen. He once posted this on rec.pyrotechnics:

 

"...Ammonium perchlorate (NH4ClO4) releases chlorine gas and only a small amount of HCl. This is important for deep blue as too much OH in the flame shifts it to a whiter colour - like more of a sky blue rather than deep indigo blue. The OH comes from the CuO + HCl -> CuCl + OH. So it is important to keep the Cl high and the HCl low..."

 

The following could also be of interest:

 

"...Potassium perchlorate leads to a potassium oxide spectrum. It also dilutes the blue, and all other "pure" colours. That APC [ammonium perchlorate] is non-metallic implies it has a low back ground spectrum, so this gives a clearer colour..."

[Boomer]

Is that Dr. Myke Stanbridge a chem Dr. or a Dr. Phil?

 

CuO + HCl -> CuCl + OH ? What molecule is OH supposed to be, hydroxylium? I go for CuO + 2 HCl -> CuCl2 + H2O.

 

Or is he speaking about the spectrum of *part* of a molecule, like the yellow/orange/red that comes from N=N bonds (diazo-colours, though these are not emmiting but ...; and CuCl is copper (I) while CuO is copper (II)? Then I still go for

CuO + 2 HCl -> CuCl + H2O + 1/2 Cl2. Confused!

[Crazy Swede]

Boomer,

I don't know anything about Dr. Myke Stanbridges background but I believe he is working with chemistry or physics! He has presented lots of personal theories that many people find strange but there is no doubt that he is a skilled pyrotechnician with lots of experience.

 

Regarding the reaction he mentiones, I totally agree that it is not totally correct but I guess he only wanted something to support what he had observed, i.e. that blue compositions containing substances with lots of hydrogen never produces as deep blue flames as compositions having the amount of bound hydrogen minimized.

 

My guess is that he is talking about the decomposition and formation of excited monovalent species in the flame. (Remember that we always talk about neutral but excited monochlorides, monooxides or monohydroxides when discussing red, green and blue emittors of coloured light in pyrotechnic flames!)