The Blues: Part 2
Copper as a ColorantBy Lee Partin
Blue: one of the most elusive of colors.
"The production of a vividly-colored flame is a much more challenging problem than creating white light. A delicate balance of factors is required to obtain a satisfactory effect." (Conkling, 151)
Colored light has a visible band related to each individual color. In the electromagnetic spectrum, the emission of blue is perceived in the visible region of between 435 and 480 nanometers. This is a very narrow band. Certain elements when heated to a particular temperature range are unique in emitting visible blue light.
Blue should not be heated above 1200 degrees centigrade. Decomposition of the color occurs above this. It is then necessary to bring the copper to a high enough temperature to excite the electrons, but low enough to keep disassociation to a minimum.
Copper and copper salts produce blue color. In the following pages, I will cover the different colorants for blue firework stars.
Sources of CopperCOPPER POWDER: Cu. Appearance: A reddish powder with a pretty metallic luster (Shimizu 112). When added to an ammonium perchlorate composition, the result should be a nice blue firework star. 5% in the formula should be enough.
Copper powder reacts with ammonium perchlorate in the presence of H2O. When decomposition occurs it can generate heat and ammonia gas. This composition should be protected from moisture.
COPPER ACETOARSENITE: (CuO)3.As2O3.Cu(C2H302)2, Paris Green. Also known as Spring Green, Imperial Green and Brilliant Green. Appearance: Shades of rich, mint green fine powder. Insoluble in water, and soluble in acid, ammonia solution, decomposes by alkali, not hygroscopic. When used in a potassium chlorate pyrotechnic formulas, with a clean-burning fuel such as shellac, it produces the best blue firework stars next to the ammonium perchlorate blue firework stars. It equally is great in purple pyrotechnic formulas. This is not to be confused with copper arsenate (Schloss green). Paris green does not decompose chlorates. Caution should be observed when using this copper salt; it is poisonous. When using Paris green you should always use a respirator with good filters and wear rubber gloves. If reasonable care is observed it is worth the effort for the result.
COPPER ARSENATE: CuHAsO3 Schloss or Schlees Green. Appearance: Lighter than Paris green with a yellowish cast. It's a fine powder, insoluble in water, soluble in ammonia and slightly hygroscopic. This product was used in the pesticide industry, and many people have confused it with Paris green. It produces a blue firework star, but it is not as intense as Paris green. As it has the problem of being somewhat hygroscopic, this can present ignition problems in firework stars. Copper Arsenate does not decompose chlorates.
COPPER CARBONATE. Basic copper carbonate occurs in two forms:
1. Malachite: CuCO3 Cu(OH)2 Appearance: Dark greenish powder, consisting of monoclinic crystals. This is usually made by precipitation. It is considered the safest for use in Ammonium Perchlorate blue firework stars, or where the composition produces a high temperature and HCl is produced in the flame. (Shimizu) When used in Perchlorate pyrotechnic formulas the addition of a chlorine donor will produce an acceptable blue firework star. Malachite does not decompose chlorates.
2. Azurite: 2CuCO3.Cu(OH)2 Appearance: Light to dark blue. This is not as a rule used in the fireworks trade. It is instead used in the paint industry. Azurite does not decompose chlorates.
COPPER CHLORIDE: CuCl2 2H2O Appearance: Light yellowish green, small crystals like sugar that are very hygroscopic. An excess of chlorine has to be present to ensure color production, PVC, Alloprene (Parlon), Saran, etc. Firework stars made from this are very hard to dry, and if left out in the drying room after dark they will re-absorb the water that dried out. If the flame is in the presence of too much oxygen, it will burn above 1200oC, in the 525 nanometer range and slip into the color green. The color produced from this is a better blue then copper carbonate. Copper chloride does decompose chlorates.
COPPER SULFATE: CuS04 5H20 Appearance: Blue stone, dark blue crystals. This copper salt was used in older pyrotechnic formulas. It has a tendency to oxidize and produce sulfuric acid; care should be taken with chlorate mixtures. Separate screens should be used with compounds made with this. Firework stars or mixtures should not be stored, but be used immediately. It can be safely used with potassium perchlorate, but firework stars made with this can be hard to light. (Weingart, 7) Copper sulfate does decompose chlorates.
COPPER OXIDE: CuO Appearance: Black, fine powder. Black copper oxide has been used for many years to produce a pleasing blue in perchlorate pyrotechnic formulas. It is not hygroscopic, and it is relatively stable. "Copper oxide emits a series of bands in the red region, and this reddish emission is often seen at the top of the blue flame." (Conkling, 160). We have used copper oxide in potassium perchlorate mixtures with magnalium, and have had safe and reproducible blue firework stars that store well. This is easily available. Copper oxide does not decompose chlorates.
COPPER OXYCHLORIDE: This basic chloride appears to have variable composition and is possibly: 3CuO CuCl2 3H2O. Appearance: Pale mint green, fine powder, soluble in acids and ammonium hydroxide, but not in water. It is formed when cuprous chloride is exposed to air. It makes a nice blue firework star but not noticeably better than copper oxide. It was used in times past because it was cheaper than other coppers. This is no longer the case. Copper oxychloride can decompose chlorates.
FuelsThere are two types of fuels that I will cover, metal and organic.
I will cover this only briefly because we do not generally use metals in blue firework stars. It can bring the burning temperature up too high for one thing, and it can "wash out" or make the blue firework star appear paler. Metal fuels include magnesium, magnalium, aluminum, and several others. Conkling stated, "A metal can be initially screened for pyrotechnic possibilities by an examination of its standard reduction potential. A readily oxidizable material will have a large, negative value, meaning it possesses little tendency to gain electrons and a significant tendency to loose them. Good metallic fuels will also be reasonably light weight, producing high calories/gram values when oxidized." (65). The coolest burning of these is aluminum Al2O3, with the consumption of only 1.12 grams of fuel per gram of oxygen. Magnalium alloy which is usually a Mg/Al ratio of 50/50 and MgO/As2O3 with only 1.32 grams consumed per gram of oxygen are also excellent fuels.
Metal fuels should only be used with potassium perchlorate composition mixtures. They will react unfavorably with ammonium perchlorate and potassium chlorate.
The Veline formulation is a great one if you like bright metal firework stars.
"The more highly oxidized or oxygen rich a fuel is, the smaller its heat output will be when combusted. The flame temperature will also be lower for compositions using the highly-oxidized fuel." (Conkling 76) This explains why we use such fuels such as lactose, shellac, red gum, and the like. I keep hearing the axiom, "Keep your blues cool", and with the knowledge we have of the temperature range of the blue light production, we understand why.
LACTOSE (C12H22O11 H2O): Lactose melts with decomposition at 200oC. Used in compositions, which are required to react at low temperatures, it is of use in the manufactures of some blue firework stars. (Lancaster 50) Lactose is also less sensitive to chlorate than sucrose.
SHELLAC: Shellac is the refined form of lac, which is the secretion of the lac insect. It is usually marketed in flakes and comes primarily from Burma, India and Thailand. It is most useful in pyrotechnics as an orange-brown powder. It has become expensive and not as readily available or used as frequently today in pyrotechnics. It burns clean without the production of excess carbons that can muddy flames.
RED GUM (Accroides Resin): A reddish brown fine powder, originally from the Kangaroo Islands off the coast of Australia. It has [largely] replaced shellac in the pyrotechnic industry. It is [one of] the main non-metal fuel source[s] today. It has a low melting point to aid in ignition.
CHARCOAL: I have used charcoal as a fuel with ammonium perchlorate. A highly carbonized sample of charcoal showed a 91:3:6 ratio of C, H, and 0 atoms (Shimizu). Charcoal may vary greatly depending on type and hardness of wood used, and it can vary between batches of the same wood. Each batch should be tested before mixing a large amount of composition. Charcoal can produce great heat, which is why it is only used in cool burning ammonium perchlorate blues firework stars.
Pyrotechnic FormulasAmmonium Perchlorate Blues
According to Weingart and many other sources, ammonium perchlorate and common copper salts produce the best blue firework stars. This is because ammonium perchlorate has a lower melting point and burns cooler than chlorate and perchlorate. The safest copper to add to this kind of formulation is copper carbonate. Care should be taken not to add finely divided metals, [such as] magnesium or aluminum to such compositions. "Corrosion of aluminum powder is accelerated by the presence of copper or mercury." (Weingart 59). In addition, it is always best to use distilled water for such firework star compositions when adding water as the solvent. It should be noted that care should be taken when storing ammonium perchlorate firework stars. Moisture can cause decomposition.
|Blue Pill Box Firework Star, Lancaster pg. 92|
|Copper Carbonate Basic||14%|
|Bruce Snowden Blue Firework Star, Pyrotechnica I|
Potassium Chlorate Blues
I personally prefer chlorate blue firework stars. The colors are clean, deep, and rich. Chlorate firework stars are easy to light, and require little heat for their ignition. Finely divided metals, or magnesium or aluminum should not be added to the firework star composition. When water is added it will attack the aluminum; the copper in the composition will aid this. The decomposition of the aluminum is an alkaline reaction; this will produce heat and gas. A buffer of boric acid could be added. However, my question is, WHY add metal at all to the blue? It only weakens the color and will make it appear paler. It can also raise the temperature of the blue firework star and cause it to go into the green range. Clean cooler burning fuels such as shellac and lactose also contribute to beautiful colors.
|Chemical Formulary Blue Firework Star|
|Bleser Blue Firework Star|
Potassium Perchlorate Blues
Considered the safest of the blue firework star compositions, it is also considered the weakest of them. Aluminum and magnalium is added to perchlorate firework star compositions to get blue electric firework stars. These metals are reasonably safe in perchlorate compositions. This is a good place for novice pyrotechnicians to start. The additions of flame enhancers will help with perchlorate firework stars. Perchlorate firework stars are harder to light.
|Shimizu 216 Blue Firework Star|
|Basic Copper Carbonate||12.3%|
|Rice starch [soluble glutinous]||4.8%|
|Robert Veline WCPB Blue|
|Magnalium 50:50 -200mesh||6%|
J. A. Conkling, CHEMISTRY OF PYROTECHNICS, Marcel Dekker, Inc. New York 1985
R. Lancaster M. A., FIREWORKS Principles and Practice, Chemical Publishing Co., Inc., New York 1972
Tenny L. Davis, Ph.D., The Chemistry of Powder and Explosives, Angriff Press, Hollywood, California
George W. Weingart, Pyrotechnics, Chemical Publishing Co., New York, Second Edition 1947
Takeo Shimizu, Ph.D., FIREWORKS The Art, Science and Technique, Pyrotechnica Publications, Austin, Texas, Second Edition, 1982
Mike Swisher, Consultation
Enjoy - DRAGON LADY
- Ammonium Perchlorate (CH5000)
- Charcoal (CH8064)
- Copper Carbonate (CH8087)
- Copper Oxychloride (CH8098)
- Cupric Chloride (CH8091)
- Cupric Oxide (CH8096)
- Dextrin (CH8107)
- Lactose (CH8169)
- Magnalium 50:50, -200mesh (CH2073)
- Paris Green
- Parlon (CH8210)
- Potassium Chlorate (CH5200)
- Potassium Perchlorate (CH5400)
- Red Gum (CH8230)
- Resin, Accroides
- Rice starch (CH8238)
- Shellac (CH8255)