10 replies to this topic

[GreenGenie]

I am a little confused over binding Aluminium compositions. From what I have read, binders require water to cause them to harden. Alcohol usually in the form of methylated spirits is sometimes used but meths contains a lot of water and it is the water that causes the binder to set.

I also read grave warnings that Aluminium should not come into contact with water as it reacts with it causing an exothermic reaction which could ignite the composition possibly causing an explosion.

What binder method is safe with Aluminium?

[Pyrogeorge]

you must use boric acid if you bind with water/alcohol to avoid the reaction.i haven't any problem.

[knackers]

your Al mesh size plays a role too, for instance, 60# is not going to be as reactive as 300#, if at all. but the general rule is 1% boric acid

edit:- it also has tell tale smell of Ammonia when it reacts

Edited by phill 63, 18 April 2009 - 11:23 PM.

[Arthur Brown]

Bind with a 25% meths in water mix added til the compound still looks dry but will just agglomerate when pressed. Much of the skill is using only just enough water to bind you are not making soup!

[GreenGenie]

Thanks guys. Sounds like good sensible advice. I understand your reasoning and it checks with what I have read elsewhere.

I have done quite a lot of reading now (though I am still very much the novice) There are quite a few aspects of pyro where I think I probably know what the correct view might be. But I do not like doubt and uncertainty. I am really keen to air these issues and have the answers spelled out to me so that I understand fully. I am grateful to the members.

[digger]

I have pretty much stopped using dextrin now in favors of SGRS. If rolling stars I use 90% water 10% alcohol until the stars are about 3mm then I switch over to 100% water.

If you are pumping stars then a good guide is 10% - 15% water. Just keep working it in and it will start to change to a slightly damp powder which is just enough to make it stick together when pressed hard, it also keeps your tools much cleaner.

If you are cutting stars then you will need to add much more water until it starts to become like a stiff dough.

Regarding the aluminium water reaction then there are a couple of options. Add a small amount of boric acid to the composition typically 1%. however the most effective solution is to add boric acid to the water you are using to bind the composition until you can't dissolve any more. This will not be much as boric acid is only sparingly soluble in water.

Edited by digger, 19 April 2009 - 09:24 PM.

[Mumbles]

I second the use of boric acid solution to wet the compositions. I've never had a reaction doing it this way. I simply make a gallon at a time. Pour a bit out, and add in some boric acid. Shake every so often, and it should be dissolved over night. I add around 150g I believe, which is 4%.

10-15% seems WAY too high for anything but charcoal streamers. I typically work in the range of 6-8% for colors, 10% for glitters, and 12% for charcoal streamers. I add the water and mix it in, press it into a cake, and let it sit for 15-20 minutes. This really helps the water to evenly distribute, and activate the binder.

There are a few things that can increase the probability of reaction. I find stars with NaHCO3 are the most likely to react. The reaction is base mediated, so you have to keep the pH in check. Flake aluminums are more likely to react. I've only had problems with stars reacting in this way when they were cut. Never pumped, and I don't frequently roll stars.

Not only should you be on the look out for ammonia, but also for H2S. All the reactions I've ever gotten had H2S, and not ammonia. If stars are heating up, it's also a bad sign.

I'm not sure what kind of denatured alcohol (meths if you will), you have in the UK, but it's very high concentration here. Generally azeotropic if not higher. There are special applications too, but those are more a result of buying off politicians than actual legitimate use.

[digger]

I second the use of boric acid solution to wet the compositions. I've never had a reaction doing it this way. I simply make a gallon at a time. Pour a bit out, and add in some boric acid. Shake every so often, and it should be dissolved over night. I add around 150g I believe, which is 4%.

10-15% seems WAY too high for anything but charcoal streamers. I typically work in the range of 6-8% for colors, 10% for glitters, and 12% for charcoal streamers. I add the water and mix it in, press it into a cake, and let it sit for 15-20 minutes. This really helps the water to evenly distribute, and activate the binder.

There are a few things that can increase the probability of reaction. I find stars with NaHCO3 are the most likely to react. The reaction is base mediated, so you have to keep the pH in check. Flake aluminums are more likely to react. I've only had problems with stars reacting in this way when they were cut. Never pumped, and I don't frequently roll stars.

Not only should you be on the look out for ammonia, but also for H2S. All the reactions I've ever gotten had H2S, and not ammonia. If stars are heating up, it's also a bad sign.

I'm not sure what kind of denatured alcohol (meths if you will), you have in the UK, but it's very high concentration here. Generally azeotropic if not higher. There are special applications too, but those are more a result of buying off politicians than actual legitimate use.

I have to say I tend to SGRS over dextrin which seems to require a little more water. This maybe just my experience with my home made SGRS.

[BrightStar]

I have to say I tend to SGRS over dextrin which seems to require a little more water.

Slightly off topic, but why the SGRS over dextrin? Are you doing clever things with torro or maybe looking for less hygroscopic stars?

More to the point, has anyone tried making metal-heavy Al stars (eg Shimizu Silver Wave) with wheat paste as well as the regular binder? I'm told it can make all the difference in preventing them crumbling when cut.

[digger]

Slightly off topic, but why the SGRS over dextrin? Are you doing clever things with torro or maybe looking for less hygroscopic stars?

More to the point, has anyone tried making metal-heavy Al stars (eg Shimizu Silver Wave) with wheat paste as well as the regular binder? I'm told it can make all the difference in preventing them crumbling when cut.

I just find that SGRS rolls better, it is far more tolerant of over wetting. But you can't dry it as quick as dex bound stars or they will crack.

Yep I have done Silver Wave (slight variation on the ali mesh sizes), lovely star, bitch to light. I have used both dex and SGRS with no real problems, both rock hard (pumped crossettes).

[Mumbles]

I like SGRS better too while cutting, but I do like dextrin when pressing(combined with gum arabic). I also agree that it takes more water to activate it though, so now I understand the higher water percentages. SGRS in my experience takes more time to activate than dextrin, so I tend to avoid it for rolling and coating burst. It's also too rubbery for me. If you over wet the comp it can tend to expand, droop, and stick to my crossette pumps.

I've used wheat paste to cut and press high metal content stars. It really does make a big difference. I use the pre-cooked dry wheat paste sold for wall paper paste. I usually mix it 7:1 water:wheat paste for pasting shells. I think it ends up around 9 or 10:1 when thinned for compositions. It should be about the consistency of whipping cream or so. It's hard to really describe. The flitter stars I make are a combination of -325 bright flake, 100-325 bright flake, and -20 flitters. Dextrin doesn't do much, SGRS is better, but they pressed much easier when wetted with the wheat paste. It just agglomerates all the flake better in my opinion.