Synthesis of YInMn Blue and Other Pigments

YInMn Blue

YInMn Blue is a pigment composed of Yttrium, Indium, and Manganese. I prepared this pigment by firing a blend of Yttrium(iii) oxide, Indium(iii) oxide, and Manganese(iii) oxide at 1200°C for 12 hours in total.

Preparation of Manganese(iii) oxide

Manganese(iii) oxide is required for this synthesis, but is not widely available. However, it can be easily prepared from Manganese(ii) oxide using a high-temperature furnace. All you have to do is heat MnO₂ at around 600°C for 6 hours. In this reaction, the oxide undergoes oxidation with oxygen gas in the atmosphere, causing Manganese to oxidize from 2+ to 3+.

After taking the product out of the furnace, you can weigh it to see if the mass changed as expected. Additionally, adding hydrochloric acid should yield brown Mn³⁺ ions in solution.

Store the Manganese(iii) oxide in an airtight container with silica gel to prevent absorption of water.

Dehydration of Yttrium(iii) oxide

Yttrium(iii) oxide is naturally hygroscopic, meaning it absorbs water from the atmosphere. It is necessary to first remove this excess water before using it to make YInMn Blue, as the water adds weight, which means that you will add too little yttrium if you directly measure it when wet.

To dehydrate this oxide, simply heat it to 600°C for 6 hours to drive out the water. When storing the oxide, keep it in an airtight container with silica gel to prevent rehydration.

Mixing powders

To prepare YInMn Blue, you must measure out and mix stoichiometric quantities of each oxide. The chemical formula of YInMn Blue is YIn_1-xMn_xO₃, where x can range from 0 to 1. As x increases, the pigment becomes a darker blue. I used x = 0.2 for my pigment.

Therefore, the chemical formula that we want to replicate is YIn_0.8Mn_0.2O₃. For every mole of Yttrium we add, we must add 0.8 moles of Indium and 0.2 moles of Manganese. Measure out powders in this molar ratio and mix them well. You will also want to grind them down into a very fine powder before firing, which I did by shaking a bottle filled with steel ball bearings. A mortar and pestle also works, but I found that the pigment often stuck to the coarse sides of the mortar, reducing my yield significantly.

After mixing and firing, the pigment should take on a blue color. Grind it up and fire it again until the color is homogenous and no discolored flecks remain.

Cobalt Pigments

I became quite interested in cobalt chemistry specifically because of the many colors that cobalt ions can undertake.

Cobalt Blue

Cobalt Blue is a historical blue pigment made out of aluminum and cobalt oxide. It has the chemical formula CoAl₂O₄.

I used a mixture of Cobalt carbonate and aluminum oxide which was fired at 1200°C for 2 hours. The powders should be mixed in a 1:1 ratio of CoCO₃ to Al₂O₃. The high temperatures trigger decomposition of the cobalt carbonate, converting it to Cobalt oxide, which subsequently reacts with alumina.

As with all fired pigments, you should grind the powders well prior to firing. I used a mortar and pestle for this, and got satisfactory results.

Additionally, you ought to be careful and not use quartz heating boats for this reaction, as the cobalt blue produced will naturally diffuse into the glass and embrittle it, as I learned the hard way. In effect, this creates cobalt blue glass.

Cobalt Phosphate

Cobalt Phosphate is a purple powder produced from the precipitation of cobalt ions using phosphoric acid. You can prepare it by mixing two solutions of cobalt 2+ and phosphoric acid.

Cobalt Oxide

Cobalt Oxide is a dark brown to black pigment which can be produced in two ways.

In the first way, it can be produced by the firing of cobalt carbonate at high temperatures, where the carbonate decomposes to release carbon dioxide, leaving behind cobalt oxide.

In the second way, it can be produced by the precipitation of cobalt 2+ ions with a hydroxide solution, producing cobalt hydroxide. Cobalt hydroxide is a blue or pink precipitate, depending on how fast you add the hydroxide. Over time, it will decompose into cobalt oxide.

Cobalt(ii) Chloride

Cobalt chloride is an interesting chemical because of its ability to change color under different conditions. Its anhydrous form is light blue, while the hexahydrate is a deep purple. It also changes color from red at room temperature to blue at high temperatures. In the presence of high chloride concentration in solution, it also undergoes a color change from pink to blue owing to the formation of the CoCl₄^2- complex.

Copper Pigments

Copper pigments are also quite interesting, as they can form nice blue pigments. They are prepared from solutions of copper 2+. The copper ions can be acquired from copper sulfate, which can be found as root killer in hardware stores.

Copper Carbonate

Copper Carbonate is a blue pigment which can be prepared from the precipitation of Cu²⁺ with sodium carbonate. Sodium carbonate can be acquired from baking soda or washing soda.

Upon precipitation, use a coffee filter to catch the solid, and leave it out to dry overnight.

Copper Chloride

Copper chloride is a soluble copper salt which can be prepared by reacting Cu²⁺ with chloride ions. These chloride ions can come from table salt or hydrochloric acid. This salt can be crystallized and appears to be a dark blue color.