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The classical ‘dark blue’ or more correctly a deep violet blue, was obtained using potassium perchlorate with a very high black copper oxide content, a precipitated sulphur and acacia gum fuel/binder, and HCB as chlorine donor… The trick is to minimise the hydrogen content of the composition as far as possible. I have posted such formulations here for general information; in particular, the Chinese warm pressed microstar formulation with minimal acacia gum: Chinese deep violet-blue microstars W% Potassium perchlorate to pass #240 39.0 Black copper oxide to pass #240 37.0 precipitated sulphur to pass #240 15.0 Hexachlorobenzene (HCB) to pass #60 6.5 Acacia gum, a top quality fine dust 2.5 This formulation is from the analysis for the Lantern “Blue Stars” multitube ground item that projects bursts of blue flowers about four metres into the air on a spray of golden firedust, etc. I can’t find the correct item number, sorry. The following method was developed to duplicate what is a very nice microstar. the formulation is not balanced for stars larger than around four millimetres in diameter… This is blended four times through a #24 mesh screen without the HCB, this is added on a fifth screening after a spraying with deionised water and even sprinkling on of the HCB. This is designed to minimise HCB dust, etc. The mix is screened a final sixth time. Making the 3 mm cylinder micro stars needs a twin-roller press and warm damp powder. A roller mill with 4″ rollers works well. The arrangement has a silicone rubber mat with many 3 mm holes, which is put between two stainless steel plates. The hard rubber mat is screed filled with damp composition while laying on the bottom plate, and is covered with the top plate and put through the roller mill, etc. The dry microstars fall out easily by gentle bending, etc… Regards, Myke. ——————————————— He answered a follow up question about substitutions with this reply: Special notes: “The use of Acacia gum is rather special for not melting during its decomposition, where its hydrogen is released as water vapour with a minimal effect on colour. I naturally tried the various combinations with many chlorine donors, including dechlorane, but it was not as good. Oddly the formulation is very tight, and even tiny changes make a very big difference in the final performance. Changing star size to even 5 mm leads to a marked decrease in performance over the 3 mm microstars.”
