[pravien]

Hi guys, i just registered in this great forum. i'd appreciate it very much to get some of my burning questions answered 

I was wondering if anyone knew how to 'beautify' a fire-wood sustained fire like those seen in campfires. These flames burn a boring orange by default, and I was hoping for a way to tint the colour of the flame for something more refreshing by adding the right stuff.

I've did google but the results seem to point toward flame colouring in lab conditions with a bunsen burner, et cetera. Is is possible to 'colour' the flame of a fire sustained by burning firewood?

Any help is much appreciated!

-praviano

[UnintentionalChaos]

Blues and greens are readily achievable in wood fires. It will never color all of the fire, of course, since you are competing with sodium and calcium salts in wood, ie. intense yellow and orange emission bands. Add a sprinkling of either copper (II) chloride or copper (II) acetate to the fire for immediate effect. CuCl2 will hydrolyze if not anhydrous and release some HCl, so the acetate is more benign.

Strontium carbonate makes brillant red flames, although I am not sure if a wood fire is hot enough to get a decent color. Maybe strontium chloride would function at lower temperatures (chlorides generally have fairly high vapor pressures).

[pravien]

Thank you for that, UnintentionalChaos. I'm glad to know achieving a different coloured flame (albeit not the entire flame) is possible!

However, how about safety issues? I'm no good with working with chemical equations to figure out what dangerous substance could potentially be released from the reaction so i'd need some help here. Thanks a lot!

If anyone has anymore ideas, please don't hesitate to contribute! Thanks in advance!

[UnintentionalChaos]

You need only a little of the salts to color the flame, since the color comes from vaporized metal ions. The color would need to be re-applied multiple times since it generally only lasts a few minutes. Soaking pieces of wood of pinecones in a strong solution of the desired salt and then drying before adding to the fire will give you the longest lasting color since more will be exposed as the wood/pinecone burns away. An impressive display of the possibilities can be done by taking roughly two parts (by weight) copper sulfate pentahydrate (tree root killer) and one part table salt, dissolving them in water and boiling down to dryness in a container you won't be using for food again in the microwave. You will have a mix of brown and white salts that is a combination of anhydrous copper sulfate, anhydrous copper chloride, copper oxychloride, sodium sulfate, and sodium chloride. This mix is powdered and sprinkled onto a bed of hot coals in a fire, turning a good portion of the flames blue-green for a short time (quite short). I realize this procedure is very unscientific, and much purer products could be produced, but for a demonstration, it will work. Ideally, you would calculate the exact amount of chemicals needed, chill the mixed solution and filter out the sodium sulfate crystals that form, then evaporate slowly to dryness and finally extract all of the copper chloride out of the mix with acetone or dry alcohol, but that is unnecessary right now. In pyrotechnics (which this is a super mild form of) it is often extremely difficult to predict reaction products since weird stuff can happen with high temperatures and unpredictable conditions. If you just avoid any really toxic metals, you should be fine. Most organic material will be reduced to carbon dioxide and water. Although chlorides, sulfates, and nitrates will release hydrochloric acid, sulfuric acid anhydride, and nitrogen oxides, respectively, the quantities you will be using shouldn't pose much of a threat unless you 1: eat the salts 2: have no ventilation (ie. the fire you are coloring is actually your furniture. You will be fine with a fireplace or campfire.) or 3: intentionally inhale huge quantities of the smoke. I've gotten too many facefuls of ammonia gas, xylene vapors, and sulfur dioxide fumes to worry about quantities of burning salts on the order of a few grams, but being careful is always good.

[pravien]

Hello again and thanks!

I've been asking around and so far people have suggested barium chloride and other group 2 salts to produce colours. Is this sound? Some have even suggested the use of potassium chloride for dramatic effects but i understand that use of potassium salts is terribly dangerous... or is there a way?

Also, how about the quantity required to sufficiently tint the colour of the flame? I'm doing a pretty large sized fire-pit so if anyone has a ball-park estimate on how much of a salt is required i'd be grateful!

Thanks in advance!

[Sam (NG)]

Potassium Salts tend to produce purple flames as far as i remember, but be careful, Potassium Nitrate and Potassium Perchlorate burn hot.

Mix Potassium Nitrate and Sugar (Sucrose) in a 5:3 ratio, then melt them carefully in a pan until you get a brown liquid, then pour into a foil mold and let it set.  Stick that in your fire and it should burn Purple with lots of smoke.

[UnintentionalChaos]

I'd deathly avoid barium anything, especially a water soluble form like that. Barium is quite toxic, worse so, IIRC, than lead. Think about breathing in worse-than- lead chloride vapor and then reconsider on that one. It is sometimes used for fireworks when people won't be inhaling it so much. Also, if you wan't to cook any food over the fire, do this before coloring it. Vaporized metal salts are nothing to let stick to food. Potassium won't do much for you, I'm afraid. It does have a purple emission line, but it's quite weak and will be easily overpowered by the sodium salts present in the wood. Case and point: wood already has a lot of potassium in it, some sodium and some calcium. When you burn it, you will not find a bit of purple in the flames since the emission line of sodium in particular is so strong. I wouldn't advise smoke-bombing your guests with KNO3 and sucrose. A tiny piece will make an enormous cloud of white smoke which will probably alert the local cops. Very little flame is produced when that stuff burns (have some in the garage) and it's obscured by smoke anyway. Potassium is much more benign than barium or copper or just about anything else you could throw in, but it won't do anything for the color. I've had success with copper before, though it needs to be in some kind of medium for the color to last. Otherwise its a 20 second blaze of blue and then nothing. I think calcium would push toward an orange flame, and it has non-toxic salts, though again, not very impressive since fire is already somewhat orangish. Boron does green as well, but would probably be obscured by the yellow since I don't think it is a strong emission. This is easiest to add as boric acid sold for killing roaches. You may want to give that one a trial run. It makes a very nice color in a blue propane flame, though I don't know if it'll work for a wood fire.

[Sam (NG)]

Fair enough, i was just going on what i'd read on the net, i've never tried colouring flames of a fire myself.

[constant thinker]

Wikipedia has a good reference.
http://en.wikipedia.org/wiki/Flame_test
Scroll down a little, and you'll see a nice table.

I've colored a camp fire a nice green/green-blue before except it was accidental. What had done was tossed a scrap of copper pipe (the stuff used for plumbing) into a fire when I was camping. It had turned the green/green-blue color for about 5 minutes, it surprised me.

I know that commercially you can buy mixtures of various salts that are intended for throwing into the fire. I've found the stuff at Walmart and fireworks stores before. I usually comes in a tube.

[Borek]

I think searching forums may help. I am more then sure this topic was already discussed at least once.

[pravien]

Wow thanks guys, you've all been a great help. Testing starts this weekend and it seems theres a lot to do.

Can throwing in the copper pipe produce consistent results? Would the flame definitely turn green-blue if I added into the fire a few of these pipes? This would be a much simpler alternative as compared to exposing my 100+ participants to the possible dangers of using the wrong chemicals!

@ Borek:  i've actually searched before posting and there doesn't seem to be anything about colour campfire flames. Thanks nevertheless!

Thanks again guys! hope to hear more from you all

[Borek]

http://www.chemicalforums.com/index.php?topic=5144.0