Copper as a colorant




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The Blues, Part 2


A couple of years ago, I helped instigate a blue-star colour contest at one of the Florida Pyrotechnic Arts Guild's spring shoots. The judges were looking for the colour that most closely approximated a blue we described as "cop light blue." That is, a blue deep enough to be a good blue colour, yet bright enough to be visible from normal viewing distances. The results of that contest as well as other blue-related information are described in a single issue of the Florida club's newsletter, The First Fire, entirely devoted to the topic of "Blue." We are reproducing the articles that appeared in that issue a series of these Bulletins with some small editing on my part. I hope you will find them useful in trying to create this elusive colour. Thanks to FPAG, Lin Collins, Mark Wilbur, Rich Ogden, Lee Partin and the authors for the use of this excellent material. Here is Part 2 of the series.


-Harry Gilliam


COPPER AS A COLORANT


By Lee Partin

Blue: one of the most elusive of colours.


“The production of a vividly-coloured 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)

Coloured light has a visible band related to each individual colour. 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 colour 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.

Blue colour is produced by copper and copper salts. In the following pages, I will cover the different colorants for blue.

SOURCES OF COPPER



COPPER POWDER: Cu. Appearance: A reddish powder with a pretty metallic lustre (Shimizu 112). When added to an ammonium perchlorate composition, the result should be a nice blue flame. 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: 3CuO*As2O3*Cu(CH3COO)2 ; Paris Green. Also known as Spring Green, Imperial Green, 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 formula, with a clean-burning fuel such as shellac, it produces the best blue next to the ammonium perchlorate blues. It equally is great in purple formulas. Paris green was originally commercially produced for the paint industry, and in one case used as a colorant for liquor. It made a fade resistant, stable against sun and weathering, paint colorant. (Shimizu 110). 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. 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 flame, but it is not as intense as Paris green. As it also the problem of being somewhat hygroscopic; this can present ignition problems. Copper Arsenate does not decompose chlorates.


COPPER CARBONATE. Basic copper carbonate and 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 blues, or where the composition produces a high temperature and HCl is produced in the flame. (Shimizu) When used in Perchlorate compositions the addition of a chlorine donor will produce an acceptable blue. 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. Very hygroscopic copper salt. An excess of chlorine has to be present to ensure colour production, PVC, Alloprene (Parlon), Saran, etc. 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 colour green. The colour produced from this is a better blue then copper carbonate. Copper chloride does decompose chlorates.


COPPER SULFATE: CuSO4*5H2O Appearance: Blue stone, dark blue crystals. This copper salt was used by the older pyrotechnic chemistry. It has a tendency to oxidise and produce sulphuric acid; care should be taken with chlorate mixtures. Separate screens should be used with compounds made with this. Stars or mixtures should not be stored, but be used immediately. It can be safely used with potassium perchlorate, but stars made with this can be hard to light. (Weingart, 7) Copper sulphate 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 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 blues 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 colour 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. Note: it has made a recent appearance as a salicylate whistle catalyst. (Partin; Pyrotechnica XVI). Copper oxychloride can decompose chlorates.

FUELS



There are two types of fuels that I will cover, metal and organic.


METAL FUELS

I will cover this only briefly because we do not generally use metals in blue stars. It can bring the burning temperature up too high for one thing, and it can “wash out” or make the blue appear paler. Metal fuels include magnesium, magnalium, aluminium, 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 oxidised.” (65). The coolest burning of these is aluminium 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/Al2O3 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 unfavourably with ammonium perchlorate and potassium chlorate.

The Veline formulation is a great one if you like bright metal stars.


ORGANIC FUELS

“The more highly oxidised 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-oxidised 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 colours. (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. Regardless, I find it much preferable to red gum, and worth the extra expense. It burns clean without the production of excess carbons that can muddy flames.


RED GUM (Accaroides 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) 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 carbonised sample of charcoal showed a 91:3:6 ratio of C, H and O 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.

FORMULATIONS




Ammonium Perchlorate Blues


According to Weingart and many other sources, ammonium perchlorate and common copper salts produce the best blues. This is because AP 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 aluminium to such compositions. “Corrosion of aluminium powder is accelerated by the presence of copper or mercury.” (Weingart 59). In addition, it is always best to use distilled water for such star compositions when adding water as the solvent. It should be noted that care should be taken when storing AP stars. Moisture can cause decomposition.

Blue Pill Box Star, Lancaster pg. 92

Potassium Perchlorate

39%

Ammonium Perchlorate

29%



Dextrin

4%



Bruce Snowden Blue Star, Pyrotechnica I


Ammonium Perchlorate

70%

Red Gum

10%



Charcoal

10%

Moisten With Alcohol


Potassium Chlorate Blues

I personally prefer chlorate blues. The colours are clean, deep, and rich. Chlorate stars are easy to light, and require little heat for their ignition. Finely divided metals, or magnesium or aluminium should not be added to the star composition. When water is added it will attack the aluminium; the copper in the composition will aid this. The decomposition of the aluminium 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 colour and will make it appear paler. It can also raise the temperature of the blue and cause it to go into the green range. Clean cooler burning fuels such as shellac and lactose also contribute to beautiful colours.

Chemical Formulary Blue Star Parts

Potassium Chlorate

5

Paris Green

3


Shellac

1


Bleser Blue Star

Potassium chlorate

65

Copper Oxychloride

12



Dextrin

5


Potassium Perchlorate Blues

Considered the safest of the blue compositions, it is also considered the weakest of them. Aluminium and magnalium is added to perchlorate star compositions to get blue electric 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 stars. Perchlorate stars are harder to light.


Shimizu 216 Blue Star

Potassium Perchlorate

60.8

Accaroides Resin

9.0



Rice starch (soluble glutinous)

4.8



Robert Veline WCPB Blue


Potassium Perchlorate

55

Cupric Oxide

15



Dextrin

4+



References:


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


The Blues, Part 3


Japanese for the ColoUr Blue


In the endless pursuit for the very best blue colour available, we consumed a large quantity of time and chemicals. I have seen what I perceived to be very good blue colour stars. But trying to make them is not easy. I will share the results with you. In addition, if you came to the spring shoot you may have seen these nice colours. After hearing a great deal about Paris Green as a blue colorant, we decided to test this opinion.


#1,2 Davis Page 85

Potassium chlorate

48

Barium nitrate

16



Dextrin

3



#3 Weingart

Potassium chlorate

50

Paris green

25


Dextrin

5



#4 Lancaster Page 92

Potassium chlorate

70

Paris green

20

Shellac.

10

Alcohol only


#5 Paris Green and Copper Blue

Potassium chlorate

50

Paris green

30



Dextrin

5



#6 Box Star

Potassium chlorate

4

Barium nitrate

4



Dextrin

1



#7 Allen Page 11

Potassium chlorate

24

Paris green

16


Dextrin

3



# 8 Allen

Potassium chlorate

24

Paris green

16


Dextrin

3



#9 Greg Dixon (Call Greg)

Potassium chlorate

?

Copper oxychloride

?



Dextrin

?



#10 Paris Green Blue

Potassium chlorate

68

Paris green

22


Dextrin

4



#11 AP Blue

Ammonium perchlorate

82

Copper benzoate

18


Results:


#1 Light blue, medium burn speed, slight residue.

#2 Was Weingart's pg. 132, same as #1.

#3 Would not light, think the stearin is too high.

#4 Very nice blue, fast burn, no residue.

#5 Nice blue, red at flame edge, light carbon residue.

#6 Very nice turquoise, medium speed parlon residue.

#7 Red flame no good, heavy carbon residue.

#8 Same as above.

#9 Nice blue, medium speed, light residue, parlon?

#10 Very nice blue clean burning.

# 11 Very good blue, medium speed. Clean burning.


Note: #6 burned too hot and went into green but it could be cooled down with lactose.


Keep in mind if you choose to use these chemicals; work in small quantities; start with 10 gram batches; always wear a respirator and gloves; keep all tools clean; and never add finely divided aluminium to chlorate. Copper Acetoarsenite (Paris Green) was used in [all?] of the tests. It does contain Arsenic. Also you must see two blues together to judge the best colour. Side by side, there is no better blue than Paris Green in my opinion.

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