“Hot Nitrated Charcoal” Stars Problem

[LiamPyro]

I attempted to make a “simple” batch of Chrysanthemum 6 cut stars using the “hot nitrated charcoal” method posted by Ned in which the KNO3 is made into a nearly saturated boiling solution, then added to the dry ingredients and formed into a patty in a plastic bag. For 350g total batch mass (192.5g KNO3) I used 85g water (78.5g is the theoretical minimum at 100 deg C for this amount of KNO3) and brought it to a boil, adding sufficient water to maintain the 85g after evaporative losses. 
 

After adding the dry chems and stirring, the paste began to thicken, and was stirred until the temp dropped to ~115 deg F then placed in the ziploc. Unfortunately, upon further cooling, the putty never solidified even though it became increasingly stiff. It turned into a sort of non-Newtonian fluid from hell! I even removed it from the bag and dried it somewhat before re-forming it, and despite being hard to the touch and requiring some force to cut through, the stars would slowly “melt” back together when allowed to rest long enough. Oddly, in this state, the star mix could be “crumbled” like a dry dough but would still exhibit fluid properties. I riced it through a screen, dried it more, then re-wet it with 75/25 water/alcohol and was finally able to get rid of the non-Newtonian fluid behavior and cut it into stars.

 

How does one avoid this problem? Is it necessary to prepare an exactly saturated (or even super saturated) solution to keep water to a minimum? Should I have included some alcohol to modify the surface tension of the water? Does the mixture have to be kept hot once mixed to allow more evaporation to take place?

[Carbon796]

A simple batch of C6 would have used RT distilled water and Dex. 

As with most things that people like to over complicate with Pyro. Your probably going to have to. Fine tune it on your end, for your materials. The materials that Ned used at that point in time. Are probably not exactly what you have on hand currently. For example.

Iirc, I believe that the nitrate soaking into the pores of charcoal myth. Was disproved awhile back.

[LiamPyro]

Yeah, you’re right. I said “simple” because the method is supposed to be straightforward and non-messy, at least the way Ned shows it. Maybe I should take this as a hint to truly keep my processes as simple as possible… 

 

If you have a link to the nitrate soaking into the charcoal pores being a myth thing I’d love to read it. This one’s been bugging me for a while!

Edited May 11 by LiamPyro

[Carbon796]

I don't, my assumption would be that I saw it on FWing. There was that guy that was analyzing metal particle shapes/sizes/mesh averages. That you could also send samples to. To have analyzed for a nominal fee. It may have been him. Or someone else that posted a document . . . from . . . Somewhere  . . . It's probably been almost a decade, since I recall seeing it.

I wasn't necessarily saying, you should keep things, overly simple. And not experiment. But often times. The traditional/time tested methods are faster and more reliable. Without an excessive amount of testing/tuning necessary. When your trying to actually get stuff done.

 

[DavidF]

A newbie once asked (on Passfire?) if they could make firework stars without any equipment like a ball mill. I theorized that it would be possible to make a supersaturated potassium nitrate solution in hot water, add the other ingredients, cool the mixture, make a dough, and cut them. Of course, I was thinking of charcoal stars. I chose Bleser's blonde streamer stares, which are basically C6 with added FeTi. It worked, but I did it more out of curiosity than anything. Years later, Ned picked up on the idea and tried it. Next thing, he's making videos about it, and testing 12" shells with this kind of stars! He came up with a 'formula' that spec'd using 88% of the charcoal weight as water. I'm not mentioning this in a 'sour grapes' way. Ned 'credited' the idea to me. Thing is, I just suggested it as an outside the box idea for beginners, not as something that was in any way better than accepted methods. One drawback is the fallout that these stars can produce if not made 'just so'. A lot of folks like that 'effect', but I think it looks dirty. Fallout is greatly reduced when the sulfur and charcoal and binder are well-screened together. Also, IIRC, the 'pot-nitrated charcoal' is a different thing that Ned came up with separately from this method- I think. 'C6 extra' comes to mind.

Fast forward, the best attribute to my method in the end was the bag! Ned ended up calling them 'baggie stars' but that's a bit of a misnomer. I use Ziploc Brand Freezer Bags. I also use the bags differently than Ned does. Ned uses dowels beside the bag as spacers to roll the patty to a specific thickness. I don't, and I disagree with doing it that way. I roll the patty out so that it slightly stretches the bag, being careful to not pop the zipper open. I've described it on this forum a few times. I also found that the bag method for cut stars is ideal for small (1 KG) batches of cut parlon stars. Past wisdom was that parlon stars can't be cut with a knife because they are too sticky. It's easy if it's done right, also discussed on this forum a few times. I've made lots of them this way.

In the beginning, the success of the pot o' goo star making method was attributed to the use of SGRS as binder. SGRS is a much more forgiving binder than dextrin when it comes to cut stars 'slumping'. There was a guy named Eugene Yurek that went on and on and ON about SGRS as a binder for charcoal cut stars, so I tried it. It worked just like Gene said it would. As time went on, I tried the bag method for cut charcoal stars using dextrin instead of SGRS, and also using room temperature water. Both methods worked. Of course they worked, that's the way they've been made for a long time! I still maintain that SGRS is more beginner friendly than dextrin when it comes to slumping. My favorite stars to make with the bag method are willow diadem stars. I make 1 kg. batches at a time, using commercial airfloat charcoal. If memory serves, I use between 300 and 330 grams of water per batch. If I have over-moistened, I can 'rescue' a batch by putting it in the fridge for a while to stiffen up and then cutting the stars on a cold aluminum slab. The stars are primed with scratch mix when cutting. They should NEVER be put in the sun! The solubility of the nitrate goes up with temperature, and the stars slump. They should be dried cool, maybe even with a fan blowing on them. My WD stars are as hard as rocks in a couple of weeks. I made these ones this way:

All the color stars were parlon stars, also made with the bag method.

[Mumbles]

85g for 350g of charcoal composition (24%) doesn't seem outrageously high for patty cut stars. When you say slumping, do you mean they didn't maintain perfect cubes, or do you mean they were fusing back together? I've made a lot of cut stars by this method. As long as they're not totally fusing back together you'll be fine. They might not drop off the paper as a thousand individual cubes, but they can usually be pretty easily broken apart with a hand full of stubborn ones after drying for a little while.

If you're looking to decrease the water, it's worth noting that it's more soluble than you're probably giving it credit for. I'll see if I can find a good one, but you should know that any solubility figure or curve you find that stops at 100C is incomplete. Boiling, fully saturated nitrate solution is probably closer to 115-120C and probably has 30-40% more nitrate dissolved in it.

For what it's worth, I've also seen information claiming that no nitrate is dissolved into charcoal pores. Very similar to Carbon, I have no recollection as to where I saw that or any concrete support to back that up.

[LiamPyro]

Wow, thanks for the thorough responses! I agree that 24% water doesn't seem outrageous. I made Bleser Blonde Streamer with this method successfully, using a slightly higher percentage of water as per Ned's video. For the C6 I used pine charcoal, and actually milled the charcoal, sulfur, and dextrin together overnight for a fast/dense burn. I think the fine particle size contributed to the problem - I've noticed that coarser BP chem mixes can tolerate overwetting much better, as I just wet some screen mixed 6/3/1 rocket fuel (1/2 and 1/2 airfloat and 80 mesh charcoal) with 38% 75/25 water/alc and riced it through a screen just fine (it was on the wet side, I'll admit, but still...).

With the C6, the strips of cut star dough slumped enough to fuse back together (see photo), but actually weren't as wet as they look. The dough was dense and took some effort to cut, and the slumping happened very slowly over the course of a few minutes. The solubility table I based my quantities on only went to 100 deg C, so you make a good point, Mumbles. Maybe I should try using less water. I also have some SGRS that I've never used, so that's an option too. 

Regarding the "nitrate dissolving into the pores of the charcoal" debate... from my experience processing various BP type fuels and stars with a variety of methods, it seems that the moisture content used in processing DOES alter the end result, whether or not it's from this alleged phenomenon. It makes sense that the KNO3 in solution would soak into the porous charcoal and then recrystallize internally, or at least adhere to the surface, effectively giving each charcoal particle its own onboard oxidizer. BP that has been wet and dried burns faster, and on the flip side, the last batch of willow diadem I made was pumped with a lower than usual moisture content (and higher pressure), and the stars barely burned at all despite being otherwise identical to previous batches. By the way - nice rockets David! I love willow diadem!

IMG_2159.HEIC

[DavidF]

Just to re-iterate- I don't think the hot water method is a better method, or even as good a method as making cut stars by the 'standard' method. In my view it was just an interesting workaround for somebody that had commercial airfloat, sulfur and prilled or crystalline potassium nitrate- but no ball mill. I have no opinion on the soaking into the pores allegations  

Regarding milling the comp for charcoal stars, I do have an opinion on that! I wanted to do a rocket volley of blonde streamer comets one year, and I milled the comp (without the FeTi). The comets burned so fast, my comment at the time was that I had milled the tails right off! The effect was ruined. Lesson learned. For a long time, I used to use homemade charcoal for everything, not wanting to pay to have commercial airfloat charcoal shipped to Canada. My charcoal stars always sucked, compared to the videos I saw of everybody else's. Eventually, a generous pyro sent me up a big (to me, anyway) bag of commercial airfloat. Bam, my charcoal stars were all good now (until I milled the blonde streamer mix). Airfloat is a mix of particle sizes, ranging from maybe 100 mesh on down. It is this mixture that gives the stars both fullness and longevity in the tails. I don't think it's just the size of the particles. I think it's also the shape. The particles are not beaten into submission as they would be in a ball mill, but rather they are just really small chunks of busted up charcoal. Anyway, I think airfloat charcoal is the best charcoal that can be used for nice charcoal star tails. If folks want to mill their mixes to save the effort of screening, I'd suggest under-charging the media and using light media like ceramic. As is often the case, I seem to be the only one with that opinion, lol. I've asked a few times about the production process for commercial airfloat charcoal, but nobody seemed to know, which is odd.

One thing about Ned's video: he counts on a 50 gram loss of water through the process, and does not top it back up.

Whenever I make charcoal based stars now in hobbyist quantities, I use the bag method. I use SGRS and room temperature water. When I roll the patty out flat and peel away the bag, the black rectangle is as glossy as glass. I cut away the edges for baby stars. When I referred to slumping, I meant that the stars would 'droop' and re-fuse back together. Slightly over-wet patties can be dealt with by using generous priming when slicing strips and also when cubing, after priming both sides. Otherwise, cooling the slab also helps. A lot of pyros suggest keeping a bit of dry comp back, to be added in case of over-wetting.

An interesting thing about SGRS-bound cut charcoal stars versus dextrin-bound: a dextrin-bound star will 'melt' if rubbed under running water, but an SGRS-bound star will wear down bit by bit. The SGRS seems to give 'structure' to the star. I mention this for no particular reason.

The picture did not open for me.

[LiamPyro]

I accounted for Ned’s water loss when figuring out my calculations, and simply started with my final water weight and topped it up just before taking it off the hot plate, instead of boiling down to the target weight. I also used a solubility table, instead of adapting the values Ned used directly. 
 

Interesting note about milling - I typically mill charcoal streamers for just 15-30 minutes to integrate without the dust of screen-mixing, starting from powdered chems and airfloat charcoal. However, I just grabbed some of the ground southern yellow pine from Fireworks Cookbook, which contains larger chips, so I figured I’d just mill everything together (except the KNO3) overnight. We’ll see how these stars turn out when they’re dry! I cut them nice and big, so a shorter duration is fine. Some claim that mixes like C6 and C8 benefit greatly from a thorough milling, in terms of their spark density, which is contrary to your observations… maybe it depends how fast they’re ejected from a shell, with milled streamers requiring higher velocities to “stretch” their denser tails longer… just speculating here. 

[Mumbles]

I was able to get the image to open. I can say with pretty high certainty that they're well on the wet side. A little sheen can be fine, but they're glistening. I can't say exactly what caused it, as I said 24% water doesn't seem outrageous. For reference, I often started at 20% water with a splash of alcohol and mixed it in and allowed to temper for an hour or so. From there I'd adjust the consistency to my liking with a spray bottle. It wouldn't be unheard of to exceed 24%. It was stored covered, but never monitored for solvent loss. This was all done at ambient temperature, and probably had some temperature loss by nitrate dissolving. Was your composition still warm or work area warm by any chance? Warm compositions are more fluid.

Everyone's materials are different. Humidity is different. Charcoal and other chemicals have different levels of moisture. All these things contribute to required additional water requirements.

I often also minorly mill most of my streamer compositions to save from the screening mess. Maybe 20-30 minutes. I was also starting with slightly granular nitrate, so it also helped with that. In terms of your comments on milled stars having faster burn times or denser spark tails, I would agree with that. However, it's not always what you want. As a point of comparison, you could compare a composition like C6 and Spider stars. They have actually pretty comparable formulas. Spider stars are often made with a milled black powder base or thoroughly milled compositions, and designed to burn fast and dense. C6 probably is too with how it was developed for use in Japanese fireworks. When they're broken hard the effect is quite impressive. I've transitioned to using Mike Swisher's spider star formula, which is not milled, and have come to appreciate the slightly slower or droopier effect as well.

When charcoal compositions are milled, my recollection is that the porous structure is broken down and starts to become lost. I wonder if starting to lose some of this structure and at least larger pores may also play a role in water requirements.

[LiamPyro]

I milled the comp with the intent of creating a spider star effect, as I also cut them large at 1/2”-5/8” for a 3 or 4 inch shell. They’re all primed and dry now so it will interesting to see how they look in the sky (broken sufficiently hard, of course).

I’ve found that wetting coarser mixtures is almost like wetting some fine sand, while finer mixtures act like putties. I think I ended up at the extreme end of putty consistency (and wound up with a non-Newtonian fluid). Re-wetting the comp with 75/25 water/IPA did fix the issue, although I didn’t track the exact solvent percentage that was in the comp at that point, so it wasn’t necessarily the inclusion of the alcohol that helped.