Green green food colorings which has been approved by the US Food and Drug Administration. Chlorophyll, the E numbers E140 and E141, is the most common green chemical found in nature, and only allowed in certain medicines and cosmetic materials. Quinoline Yellow (E104) is a commonly used coloring in the United Kingdom but is banned in Australia, Japan, Norway and the United States. Green S (E142) is prohibited in many countries, for it is known to cause hyperactivity, asthma, urticaria, and insomnia. To create green sparks, fireworks use barium salts, such as barium chlorate, barium nitrate crystals, or barium chloride, also
Barium borate 1 GW/cm at 1064 nm and 500 MW/cm at 355 nm. Beta barium borate, β-BaBO, is a nonlinear optical material transparent in the range ~190–3300 nm. It can be used for spontaneous parametric down-conversion. Its Mohs hardness is also 4.5. Barium borate has strong negative uniaxial birefringence and can be phase-matched for type I ("ooe") second-harmonic generation from 409.6 to 3500 nm. The temperature sensitivity of the indices of refraction is low, leading to an unusually large (55 °C) temperature phase-matching bandwidth. Barium borate can be prepared by reaction of an aqueous solution of boric acid with barium hydroxide. The