18 replies to this topic

[Gary]

Hi, given that lead tetraoxide is rather nasty and toxic, and that 200g or so of bismuth trioxide will burn a substantial hole in your wallet, I was wondering whether it is possible to create a crackling microstar effect or an equivalent effect by experimenting with combinations of various other metal oxides ( such as chromium trioxide, tin (2/4) oxides, vanadium pentoxide, cobalt(2) oxide, copper(2) oxide, etc) mixed with magnalium, aluminium or magnesium?
Or is the crackling effect only achievable using the standard copper(2)oxide, lead tetraoxide/bismuth trioxide and magnalium? I have noticed that the crackling microstar (or dragon's egg) formula is essentially a thermite-type of chemical reaction, using oxides of heavy metals. What is so special about magnalium (MgAl) in this case- why can't aluminium be used instead?
Would tin (2or4) oxide be an effective, but less toxic, substitute for lead tetraoxide? Perhaps someone might like to try this out and report back on their findings?

Edited by Gary, 10 October 2008 - 08:29 PM.

[pyrotechnist]

I find that MgAl can crackle a little on its own when heated up or mixed with some bp.

[digger]

I seem to remember in dark corner of my mind that there is a sodium thiosulphate based crackling microstar formula. If you manage to dig it up let me know.

[Mortartube]

I find that MgAl can crackle a little on its own when heated up or mixed with some bp.

Most of the British manufacturers used to use large mesh Mg/Al in their garden crackling fountains. I think it was Standard who had the crackling cauldron, a green fire with crackles of silver spitting out.

I have recently made some BP based cut stars with 15% Mg/Al added (around 40 mesh. I was given it so cannot be precise). . You can just hear the crackle when they eject from a rocket at about 30m.

This is the formula I used. It is not a take your breath away star but an experiment. I did cut stars but made them too big. They are quite slow burning. 8 or 9mm would be about right.

50% KNO3

20% S

10% C

15% Mg/Al

5% Dextrin


Add water. Mixed to dough consistency in ziplock bag and cut.

Edited by Mortartube, 11 October 2008 - 10:38 AM.

[Mortartube]

I forgot that I had this saved. I have not tried this but I will post the formula the man in question posted. He says NC lacquer is Very important for loud crackling. Here's the video:

http://n-joy.cz/vide...qjvuvpe94nyc5j/

I will post both the original formula this guy worked from and his own modification

Original

Potassium Nitrate 44.88
Sulphur 14.28
MgAl -200 mesh 14.00
Antimony Trisulphide 10.5
Airfloat Charcoal 8.84
Copper (II) Oxide 4.5
Dextrin 3



Modification for NC

KNO3 45
S 16
pine charcoal 9
Sb2S3 black 11
CuO 5
Coarse magnalium 14
8 - 10% NC paste for binding

Edited by Mortartube, 11 October 2008 - 10:39 AM.

[wjames]

Most of the British manufacturers used to use large mesh Mg/Al in their garden crackling fountains. I think it was Standard who had the crackling cauldron, a green fire with crackles of silver spitting out.

I have recently made some BP based cut stars with 15% Mg/Al added (around 40 mesh. I was given it so cannot be precise). . You can just hear the crackle when they eject from a rocket at about 30m.

This is the formula I used. It is not a take your breath away star but an experiment. I did cut stars but made them too big. They are quite slow burning. 8 or 9mm would be about right.

50% KNO3

20% S

10% C

15% Mg/Al

5% Dextrin


Add water. Mixed to dough consistency in ziplock bag and cut.

im gonna try that for a few of my rocket headers.....need to get some dextrin first.....ive got AL granules here that are 20 mesh...they'll be alright won't they ?

[Mortartube]

All I can say is give it a go. Do you have Al granules or Mg/Al granules.

Assuming it is just Al you have. You are unlikely to get a crackle with just Al. Having said that just make a small experimental batch and see. I would suggest thet you add an additional 1% Boric acid as it is a pot nitrate/Al mix. Nothing is likely to happen with Al that big but always err on the side of caution.

I make my own dextrin. There is lots of info out there inc Youtube. Basically roast cornflour gently, stir ocasionally until you get a nice honey coloured powder. That's it.

[wjames]

yeah, i have some MG granules...about 80g.....i get free samples of most things from my supplier.

i'll make some dextrin tommorrow....

[Gary]

The logic of using an oxide of tin (available from pottery suppliers) is that it is in the same chemical family as lead, and both metals have similar chemical properties (both Pb and Sn are group 4 elements of the periodic table, for those of you who are familiar with chemistry). If you wikipedia Dragon's Eggs, you'll find that it is a requirement that the crackling dragon's egg effect contains a heavy metal oxide, such as lead tetraoxide or bismuth trioxide or subcarbonate.
So, if anyone has tin (2 or4) oxide, it might be worth making-up a small experimental batch, substituting lead tetraoxide or bismuth tetraoxide for tin oxide. If it works, let me know.
The formula would contain: SnO2 (in place of Pb3O4 or Bi2O3), CuO and MgAl.

[pyrotrev]

Interesting you should mention that Gary, the same thought had crossed my mind, looking at the thermodynamics, the Tin (IV) oxide looks the better bet, though not so easy (or cheap) to obtain. On my "to do" list.

[pyrotechnist]

Wait don't they sell tin oxide at pottery supply shops within there oxides section? or failing tin can zink oxide be used or any type of oxides?

Edited by pyrotechnist, 12 October 2008 - 08:45 AM.

[Mortartube]

You must be careful with Tin oxides as Tin Dioxide in particular can create Stannic acid and you don't really want unwanted acids floating around in Dragon egg mix.

[Arthur Brown]

Also note that tin is forbidden as a marine antifoulingingredient because it is too toxic!

[Gary]

Also note that tin is forbidden as a marine antifoulingingredient because it is too toxic!

True, but tin is not as toxic as lead, otherwise the food industry would'nt use tin to coat iron food cans, and tin compounds would'nt be included in the formula for some toothpastes! The tin compound that was once used as a marine antifouling agent was tributyl tin, an organotin compound with a high bioavailability. Inorganic tin compounds are far less toxic.

[pyrotrev]

Does anyone know if the tin oxide potters use as an opacifier is the (II) or (IV) form?