31 replies to this topic

[PyroNitrate]

Some more very useful information taken off www.unitednuclear.com

Measuring & Weighing
Judging from email messages, the most common point of confusion for those just getting started in pyrotechnics seems to be measuring & weighing.
To begin with here are two important points:
1. EVERYTHING is measured by weight, not by volume.
2. The amounts of chemicals in ALL formulas are in percentage (all the parts total up to 100).
Now we'll explain what these 2 points mean:

For example, lets say you have the following formula:
( this isn't an actual formula for anything )

Zinc Dust 50

Sulfur 50


This simply means this mixture is made from 1/2 Zinc Dust and 1/2 Sulfur Powder
(50% Zinc Dust & 50% Sulfur Powder).
You can mix 50 grams of Zinc & 50 grams of Sulfur, or 50 ounces of Zinc and 50 ounces of Sulfur, 100 grams of Zinc & 100 grams of Sulfur, or even 200 tons of Zinc and 200 tons of Sulfur.
All the measurements are 50% of each chemical, and they will all work.
You CANNOT use 1 Tablespoon of Zinc and 1 Tablespoon of Sulfur, or 1 cup of Zinc and 1 cup of Sulfur.
Why? Because these are VOLUME measurements.
The reason is that different chemicals weigh different amounts.
1 Tablespoon of Zinc weighs 68 grams and 1 Tablespoon of Sulfur weighs 12 grams.
In the correct formula above there are equal amounts of Zinc & Sulfur. If you measured by volume, say 1 Tablespoon of each, you would wind up with over five times more Zinc by weight than Sulfur.
Your formula wouldn't work.
To make things worse, volume measurements are not constant. A tablespoon of Zinc dust may in fact weigh 68 grams today, but may weigh 50 grams or possibly 75 grams tomorrow. Why?... because fine powders compact when they sit around (making a tablespoon of it weigh more than it did before), and "fluff up" when disturbed or shaken (making a tablespoon of it weigh less than it did before).
Only weight measurements can be used in chemistry & pyrotechnics.
ALL formulas are measured by weight, usually in grams.

Here's an actual formula for a white star...

White Star
Potassium Nitrate
64 %
Antimony Sulfide
14 %
Sulfur
18 %
Dextrin
4 %

Make things easy on yourself... there are no complex calculations necessary.
To make the above formula, you would just mix 64 grams of potassium nitrate, 14 grams of antimony sulfide, 18 grams of sulfur and 4 grams of dextrin.
If you wanted to make twice as much... just double all the numbers.
If you want to make half as much... just cut all the numbers in half.



Now that you've got how to measure chemicals down, we need to talk about accuracy.
You CANNOT use a cheap spring-type postal scale for measuring chemicals.
If you want to get involved with pyrotechnics, you need the proper tools, and to measure the various amounts of chemicals in these formulas, you need an accurate Gram scale, preferably accurate to 1/10th gram, although a scale accurate to 1/2 gram is still usable.
Digital Gram Scales and Triple Beam Balances are your best bets.

Hope this helps

[BigG]

Good points. Just to add that it is allowed to write formulas by parts.
For example, 21 parts KNO3, 4 parts charcoal means that for every 21 parts of KNO3 you need to mix 4 parts of charcoal. The parts must be equal. So you can have 21 grams of KNO3 and 4 grams of charcoal (part = 1 gram), and you can also have 42 grams KNO3 and 8 grams charcoal (when a part is 2 grams).

BigG

[Rhodri]

Well stated BigG.

[zanes]

but my triple beam blance (and most others i see) are only accuarate to 1gram!!

[BigG]

Then mix larger quantities. A mistake of a gram in 10 grams composition is a 10% mistake ? too large. The same mistake of gram over 200 grams composition is only 0.5% error. Much better. I have a digital scale with 0.1g accuracy. You can get similar scales at prices not higher the 40-50?

BigG

[Rhodri]

Too right. Maplins sell digital balances for around ?50. I can honestly say that it's one of the best investments I've made regarding my hobby of pyro.

Try www.maplin.co.uk (this link here is typed not embedded so you'll have to copy and paste).

Search for "scales" there's one there at the top of the list for ?49.

WELL worth the investment.

[firedust2004]

I recently bought a digital scale from maplin. It was on offer for ?19.99 (normal price ?49.99) I just had to get it . It measures up to 200g with a resolution of 0.1g which is fine and I never mix chemical amounts greater than 100g at a time anyway.

[mnementh]

Hi guys,
for accuracy, check Ebay.

In the search box, type in digital scales. You'll get absolutely hundreds of hits with .1gram accuracy.

You should be able to get 500 gram scales at .1 gram accuracy for less than ?25

Sandy

[sizzle]

Indeed eBay has many auctions and Buy It Now's for digital scales, I got a 250g max, 0.1g accuracy scale for ?8.50. Amazing deals!

[Draco_Americanus]

I allmost would not recomend the dirt cheap scales as they can be unstable and give you 3 diffrent readings for the same item if measured 3 diffrent times, I just replaced one of my el-cheapo digital scales with a less el-cheapo Ohaus JE500. They jury is still out on how much I like that one but it's better then the .01g accurancy pocket scale.
anyway thats my 2 pennys

[sizzle]

Well, I always do 2 reads for accuracy when measuring and I haven't found any difference yet, is it possible your ones were just faulty?

[GuiltyCol]

This might be a silly question cos I think I've already answered it in my head, but anyway: Is it not advisable to check whether your scales are accurate? Ok measuring the same thing 3 times and getting 3 different results is not good, but what if the alleged 0.1 gram accuracy digital scales from eBay for ?8.50 actually measure 10g as 15g? Is that important?

The obvious answer is yes! But then not if you measure EVERYTHING on the same set of scales. Assuming that is that the scales inaccuracy is linearly proportional with weight. In the above example it over read by 50%, as long as everything is over done by 50% then that's fine, the proportions of everything will be the same. But what if it always weights 5g too much, whether it should be 10g or 100g? Then you're in trouble it seems to me.

My point is that considering what we're doing here: mixing chemicals to make stuff go POP! Would it not be a good idea to at least get our most important measuring kit calibrated and/or checked on a regular basis? I suppose the purchase of a set of calibrate weights would do it, so you could test yourself. Do people do this, or am I being paranoid?

[fishy1]

This might be a silly question cos I think I've already answered it in my head, but anyway: Is it not advisable to check whether your scales are accurate? Ok measuring the same thing 3 times and getting 3 different results is not good, but what if the alleged 0.1 gram accuracy digital scales from eBay for ?8.50 actually measure 10g as 15g? Is that important?

The obvious answer is yes! But then not if you measure EVERYTHING on the same set of scales. Assuming that is that the scales inaccuracy is linearly proportional with weight. In the above example it over read by 50%, as long as everything is over done by 50% then that's fine, the proportions of everything will be the same. But what if it always weights 5g too much, whether it should be 10g or 100g? Then you're in trouble it seems to me.

My point is that considering what we're doing here: mixing chemicals to make stuff go POP! Would it not be a good idea to at least get our most important measuring kit calibrated and/or checked on a regular basis? I suppose the purchase of a set of calibrate weights would do it, so you could test yourself. Do people do this, or am I being paranoid?

i don't have calabrating weights, but new ?2 coins work for me.

[GuiltyCol]

Sounds great, except I don't know what new ?2 coins are meant to weight? And is that different from "old" ?2 coins? Sounds like I'm being anal about this, but with all the warnings on this forum about not being accurate when mixing chemicals, just seems risking your life to what might be a second hand weighing machine, might not be awefully sensible.

[fishy1]

Sounds great, except I don't know what new ?2 coins are meant to weight? And is that different from "old" ?2 coins? Sounds like I'm being anal about this, but with all the warnings on this forum about not being accurate when mixing chemicals, just seems risking your life to what might be a second hand weighing machine, might not be awefully sensible.

14g.

and by "new" ?2 coins, i mean the shinier ones, as the older corroded ones may weight a little bit less/more than 14g.