Gearing up for my first crackle experience

[Uarbor]

I have done my due diligence but I still have some questions about making Crackle. First off how thick should my nitrocellulose lacquer be for this project? Mine is like honey I have a feeling I should dilute it with a little more acetone. I am aware of the accepted Crackle formula with 75% bismuth trioxide. My next question is about the Chinese formula floating around that is 68% black copper oxide 30% magnalium and only 8% bismuth trioxide. Is this worth trying? It sure would save on the Bismuth. Any info or tips would be greatly appreciated

[SharkWhisperer]

Honey viscosity is fine. If you are aiming to get to 5% final NC concentration, even using 10% NC lacquer much of your processing time is going to be spent waiting for acetone to evaporate. I stopped aiming for 5% final and go with around 2.5% NC final, with no obvious effect on crackle character and using half the NC/acetone.

 

Re formulations; I almost immediately switched from the classic high-bismuth formulation to a 35:35 CuO/Bi2O3 formulation, again with no impact on final product functioning. I did this when bismuth was super pricey, though now FWC had dropped the price down to $15/pound, which is closer to the CuO that has gone up in price in recent years.

 

Never tried straight CuO...

 

Also started testing using phenolic resin in place of NC for binding, which was promising, but got sidetracked. I'm not convinced NC is necessary in DEs and highly doubt that Chicom crackle uses NC or high % of Bi2O3 in their very functional crackle and DEs. Maybe check USAPyro's old thread on No-NC crackle for ideas. My preferred processing steps are also outlined in some thread a few years old, as are others'.

 

Crackle's a hoot, though, and your next scrap gerb will be very eventful!

Edited April 19, 2022 by SharkWhisperer

[Richtee]

I have been using the 35^2 formula too. I make 33 grambatches... 12.5/12.5/8.3333333. That .3333 bugs the HELL outta me

 

Honey is good. Maybe a touch thinner by the time you pour them... acetone’s fast.

 

It’s kinda amazing the snap ya get out of a tenth gram or so.

[Uarbor]

Well my chemicals came in and I mixed up a batch of 37.5 / 37.5 / 25. I took a little less than 1/8 teaspoon of the powdered mix and put it on a piece of sheet metal to test. Lit it with a torch for a second and it's smoldered for about a second and a half and kapow. Scared the crap out of me LOL my wife heard it from in the shower LOL sounded like a pistol shot. I can't believe it was so loud unconfined I can't wait to bind it up with my n.c. lacquer. I assume it won't be that loud in a Micro Star form. I am pretty fascinated with it. I would love to know the scientific reason it does this. Edited May 1, 2022 by Uarbor

[Richtee]

Scared the crap out of me LOL my wife heard it from in the shower LOL sounded like a pistol shot. I can't believe it was so loud unconfined I can't wait to bind it up with my n.c. lacquer. I assume it won't be that loud in a Micro Star form. I am pretty fascinated with it. I would love to know the scientific reason it does this.

HAH! I bound mine and tested a .25” X eighth inch or so square similarly. SOMMABEEECH! Blam! When ya see that glow, she gonna blow

 

And I too am curious on the technical explanation...even if I won’t understand all of it I DID have to take 2 semesters of chem at college and 1 class in HS but yeah, that was 30+ years ago, and I was not all that good at it even then hahaha

Edited May 2, 2022 by Richtee

[Uarbor]

HAH! I bound mine and tested a .25 X eighth inch or so square similarly. SOMMABEEECH! Blam! When ya see that glow, she gonna blow

 

And I too am curious on the technical explanation...even if I wont understand all of it I DID have to take 2 semesters of chem at college and 1 class in HS but yeah, that was 30+ years ago, and I was not all that good at it even then hahaha

I just made my first batch of micro Stars. I think they are dry now I cannot detect the smell of acetone. Although I must say I could have Ford little piles of powder composition out and let it fill it was all used LOL

[Uarbor]

Here's a test. 1/8 teaspoon in paper.

 

[Uarbor]

Seems 👍 Edited May 3, 2022 by Uarbor

[Richtee]

Fun stuff! I made a post on coating a hunk of visco with it. Damned entertaining! As you seen..it DOES tend to jump around tho.

[Uarbor]

Fun stuff! I made a post on coating a hunk of visco with it. Damned entertaining! As you seen..it DOES tend to jump around tho.

I did see that. It looked like fun it made me want to dip some e matches in that stuff and set them off at will with no warning of a fuse, keep my bonfire guests on their toes LOL Edited May 4, 2022 by Uarbor

[Uarbor]

I have been reading up quite a bit here and elsewhere and falling just short of forking over fifty bucks to Ned Gorski. And I read that larger Stars require larger mg/al. I read somewhere that you can make big ones that are more like a salute a novelty item or something like half inch? I have some 20-60 mg/al. I might make that my next project I like small devices. I think I'll make a star gun shooting one big slug of crackle and trying to get it to go off just once using all the composition. Any advice is more than appreciated Edited May 4, 2022 by Uarbor

[SharkWhisperer]

I have been reading up quite a bit here and elsewhere and falling just short of forking over fifty bucks to Ned Gorski. And I read that larger Stars require larger mg/al. I read somewhere that you can make big ones that are more like a salute a novelty item or something like half inch? I have some 20-60 mg/al. I might make that my next project I like small devices. I think I'll make a star gun shooting one big slug of crackle and trying to get it to go off just once using all the composition. Any advice is more than appreciated

It's possible you might run up against a wall in trying to balance MgAl particle size to DE size. I've used -60 MgAl (mixed mesh; lots of smaller particles along the spectrum) for microstars and up to about 1/4"-3/8" cores (6-10mm for our metric-based folks) with good effects. Unprimed cores when ignited would be loud but blow small chunks of unburned comp around. With a good thick hot prime they went off in entirety. Never tried larger MgAl, so will be interesting to hear how it goes. I habitually add 5% Al (fine atomized or smallish flake both seem to work fine) to DEs, and adding it into your large eggs might help keep the burn/smoulder going long, hot, and uniformly enough to get complete response from the whole DE mass. That, too, is speculation. At a certain size, besides "because I can", I'd imagine simple 70/30-based small inserts would provide more reliable large bursts than comparatively heavier (and more expensive) big-ass DEs. Wasn't that you who improvised a "crackle" shell last year with a handful of 1.4g firecrackers, hah ha? Anyways, good luck!

[Mumbles]

The metal size controls the delay time. Larger metal particles, longer delay generally speaking. On one end of the spectrum if the metal particles are too fine, the granule transitions from delay to explosion too fast to the point you get multiple explosions per grain. This leads to kind of a sizzling effect. On the other end of the spectrum, if the metal particles are too big, the granule can be delay only and basically just glow. It never gets over the hill or cools off too much, and never explodes.

[johnnypyro]

After a couple of failed attempts I managed to get DEs working.

 

Composition was 37.5/37.5/25. Dissolved 10%/w double based shotgun propellant in acetone (stir, leave to stand covered for 30 minutes, and then stir again). I let the acetone evaporate until I had a honey like consistency and then added the powder composition forming the dough which I then pushed through a wire mesh.

 

In my limited experience the key is the MgAl, which needs to be good quality (50:50).

 

I used 150-250 mesh MgAl. At this size, 10 mesh is a bit too small, 8 mesh is better. Any smaller pieces can be rewetted with acetone and redone through the mesh.

 

Prime with BP

[Uarbor]

After a couple of failed attempts I managed to get DEs working.

 

Composition was 37.5/37.5/25. Dissolved 10%/w double based shotgun propellant in acetone (stir, leave to stand covered for 30 minutes, and then stir again). I let the acetone evaporate until I had a honey like consistency and then added the powder composition forming the dough which I then pushed through a wire mesh.

 

In my limited experience the key is the MgAl, which needs to be good quality (50:50).

 

I used 150-250 mesh MgAl. At this size, 10 mesh is a bit too small, 8 mesh is better. Any smaller pieces can be rewetted with acetone and redone through the mesh.

 

Prime with BP

I always seem to come up with my own methods for everything. I make the dough and then I great it not press it through a 4 mesh screen directly into the prime. Then I sift out the pieces. All the pieces that are oversized get pressed through a kitchen strainer back into the Prime. This helps keep everything from sticking together. And they work fantastically and by the way I used 200 / 375 mg / al because that's what I had on hand. Edited June 22, 2022 by Uarbor