My stars crackled and crumbled

[50AE]

So this is what I did:

 

I made a small batch of forli green. It's made of

50 Ba(NO3)2

20 MgAl

12,5 PVC

10 Sulfur

5 Gum arabic

3,5 Red gum

 

The MgAl was fine, +175 mesh. The gum arabic was dissolved in water and then was added to the mix. It didn't hold quite well, like bright Al compositions don't, so I quickly made a little wheat paste from flour and added it to the mix. It held nicely, so I cut it into cubes 8*8mm.

The cubes were left to fully dry.

Afterwards, it was time to prime them. I started with a layer of green mix +5% MgAl and then a layer of meal powder. The spraying solution was gum arabic.

24 hours afterwards, I went to check them. To my horror, they had crackles and when I took one, the prime flaked off. Others crumbled in half. When I shook everything... oh my goodness.

Can you help me find out what is the reason for this? I have made other metallic colored star comps, I've also used wheat paste on other comps, but never had this issue. Maybe a bad combination of chemicals?

[FREAKYDUTCHMEN]

Why don't you use dextrin?

[Mumbles]

Was the gum arabic actually dissolved, or just suspended in water? Unless it was fully dissolved (clear solution), you may not have gotten the binding benefits of it. From the sounds of it, you would have had to make a solution approaching or exceeding 25% w/v. I really haven't a clue as to the upper limit of it's solubility. There is always the ubiquitous question of are you positive the stars were dry? Gum arabic solutions, like shellac, can film over and take longer to dry than straight water/dextrin binding.

 

As Freakydutchman alluded to, I always use a combination of dextrin and GA in my compositions if I intend to bind with GA. Gum arabic, at least in my experience, provides relatively little wet strength to the compositions, which is where the dextrin comes in handy.

 

The other posibility is that you have poor quality gum arabic and the magnalium was attacked. This may or may not give off an odor. It should dissolve to a clear to perhaps slightly yellow solution. I've had issues using gum arabic and magnalium in the past, but this was primarily with glitter comets. I've still yet to quite figure it out. Mike Swisher says that it should be fine, if not actually protect the metal, but several others on passfire noted some similar issues. The tail was short and sparse, and the effect all but killed.

[MadMax]

Here's a thought... You may want to add 20% or so of methyl alcohol to the water. Since there is red gum in the star it too will act as a binder in the presence of alcohol. Just don't add too much or the GA will get all jacked up. The alcohol is also nice because it is a surfactant and will make the water evaporate quicker.

[50AE]

I was out of dextrin and I was binding with GA only.

 

1. Mumbles, the GA was completely dissolved.

I know GA stars are tricky, they can appear dry why they aren't. But I checked them by scratching the surface inside a star.

 

2. MgAl attacked, this is a possibility. I don't know what do you mean by "smelly", but there's always a very slight mix of red gum/ammonia odor, when the stars are wet.

My gum arabic does make a clean yellow solution, it just has pieces of hay in it.

[FREAKYDUTCHMEN]

You just can not substitute one binder with the other, binders all have their own characteristics. The most commonly used binder still is dextrin and i think this is because of good reasons. I've got a couple formula's from a guy from Malta and those were all with dextrin, something you wouldn't expect I think.

[50AE]

Let me tell you that the problematic formula calls for gum arabic only and not any dextrin.

[pyroguy1960]

You probably would have better off ditching that GA, upping the red gum to 5% and used denatured alchohol as a solvent. I've used that binder/solvent combination a few times and it's always worked well for me.

 

 

[FREAKYDUTCHMEN]

Let me tell you that the problematic formula calls for gum arabic only and not any dextrin.

Who made that formula? XD

 

ahh i see, forli did...

Edited May 10, 2011 by FREAKYDUTCHMEN

[50AE]

Alright, I will use dextrin next time, but is there any warranty the crackling won't occur again? What could be the reason for it?

Or I should ask the experts on passfire?

[pyroguy1960]

If you bind it with water and dextrin or red gum and alcohol it won't happen.

 

The reason is you didn't have a sufficient binder/solvent combination in your comp.

[50AE]

The reason is you didn't have a sufficient binder/solvent combination in your comp.

 

What do you mean? If you say that GA is inferior to dextrin, you are wrong.

GA alone makes very hard stars.

I've bound many colored compositions with GA only and I can say nor dextrin nor SGRS can match the same hardness.

[pyroguy1960]

Ok than continue using the GA and ignore the post.

 

I have personally found that GA not only has special requirements in the way its used, but its also hard to find good quality GA. You may have a bad batch of GA?

 

If I want a hard star using simple methods I use dextrin or red gum and it works, that is all I know. Furthermore I can guarantee with almost 99% certainty, that if you add 5% dextrin to that comp and bind with water or you make the red gum 5% and bind with alcohol you will end up with hard stars that won't crumble when they're fully dried.

 

Why it failed in the first place, I can't speak to. So perhaps I wasn't giving a reason, just a solution. My Bad.

Edited May 10, 2011 by pyroguy1960

[dagabu]

What do you mean? If you say that GA is inferior to dextrin, you are wrong.

GA alone makes very hard stars.

I've bound many colored compositions with GA only and I can say nor dextrin nor SGRS can match the same hardness.

 

Sooooo, you dont want to fix the issue, you just want to vent? Thats fine but why dont you attempt to pretend that you are receptive to the ideas that others have? I promise that the stars will not change just because you are disappointed in them.

 

We all have stars that leave us wanting, I have stars that STILL have to loose the last 2% of moisture and they have been drying for 20 months. Talk about locked in moisture!

 

-dag

[50AE]

Of course I want to fix the issue, but I refuse to accept that GA is a weak binder, at least mine. I cut myself on a GA binded star once...

I aggree that 5% of dextrin make the stars hard enough. So, I will wait a while to buy some, because my dextrin's supplier has business right now.

Edited May 10, 2011 by 50AE

[pyroguy1960]

I put GA in the category of SGRS, touted to work wonders, but you have to know something special to make it work properly. That's just my experience anyway....the dex always worked, so I never felt the need to look elsewhere.

[dagabu]

Of course I want to fix the issue, but I refuse to accept that GA is a weak binder, at least mine. I cut myself on a GA binded star once...

I aggree that 5% of dextrin make the stars hard enough. So, I will wait a while to buy some, because my dextrin's supplier has business right now.

 

In the USA we have a saying: If it walks like a duck and quacks like a duck, it's probably a duck.

 

If you did everything the way it is supposed to be done and it failed to bind, look at the binder. This is the key to troubleshooting and the root of Occam's Razor, the principle that generally recommends selecting the competing hypothesis that makes the fewest new assumptions, when the hypotheses are equal in other respects. For instance, they must both sufficiently explain available data in the first place.

-WP

 

First thing to do is make a KNOWN star using the GA, if it fails to bind.... Well, you know the rest

 

-dag

[50AE]

Good answer dagabu

 

A known formula with GA? The most of the formulas I know are bound with dextrin, but some increase their hardness by wetting them with a GA solution.

With GA, I have bound only colored stars:

-Organic blues - my formula, forli and shimizu blue

-organic red, chlorate hardt 2

-organic orange, Pihko 2

 

Never used it on tailed stars or glitters, becase I know it ruins the effect.

[dagabu]

Well, you appear to be at a crossroads. Which road are you going to take? Try the GA in another comp similar to the one that failed or try Dextrin?

 

-dag

[burningRNX]

Maybey your gum arabic soln didn't redisolve the dry stars upper layer (fast) enough to fully bound the prime layer?,

[Peret]

I aggree that 5% of dextrin make the stars hard enough. So, I will wait a while to buy some, because my dextrin's supplier has business right now.

I haven't bought any dextrin in my life, apart from a few ounces that came with the Turbo Pyro kit. It's so easy and cheap to make. Just roast any pure food starch (cornflour, corn starch, arrowroot etc) on a tray at 350F, stirring occasionally, for a couple of hours or until it goes straw colored right through. Test to see if it's done by dropping a spoonful into a glass of cold water. If it turns into a sticky ball of toffee, it's done, and when you try and clean the glass you'll know why it's considered a good binder.

[DeepOvertone]

I haven't bought any dextrin in my life, apart from a few ounces that came with the Turbo Pyro kit. It's so easy and cheap to make. Just roast any pure food starch (cornflour, corn starch, arrowroot etc) on a tray at 350F, stirring occasionally, for a couple of hours or until it goes straw colored right through. Test to see if it's done by dropping a spoonful into a glass of cold water. If it turns into a sticky ball of toffee, it's done, and when you try and clean the glass you'll know why it's considered a good binder.

 

I agree. I dont see why anyone would buy dextrin since its so easy and cheap to make.

[pyroguy1960]

Because it's so easy and cheap to buy

 

 

[Mumbles]

The purchased stuff is also far superior to homemade as well. Once you try some good commercial dextrin, you'll be spoiled away from making it yourself. Trust me, I was in your camp for a long time too. If you have a few people to split up a reasonable sized order, the price drops to almost the level of corn starch from the store, and without the hassle of cooking or cleaning up.

[dagabu]

I bought a 20# box from Cracker a while back for a buck a pound, corn starch was $1.09 at the time. That was a real no-brainer. I agree with Mum, the commercial stuff mixes easily, no lumps, binds better and makes for very hard stars.

 

-dag