Potassium Chromium(III) Disulfate Dodecahydrate
Potassium Chromium Alum · Chromium Alum · Chrome Alum · Alum
Description
It is an excellent option for inexperienced growers because it is undemanding in its growth conditions.
It is also possible to grow a purple crystal by mixing Potassium Chromium(III) Disulfate Dodecahydrate with more transparent alums, such as Potassium Aluminium Disulfate Dodecahydrate. Depending on the concentration of Chromium(III) ions in the solution, the crystal color may vary from light purple to black.
Requirements
Our team strongly recommends purchasing Potassium Chromium(III) Disulfate Dodecahydrate directly rather than attempting to synthesize it yourself. This compound is commonly sold under the names "Chromium Alum", "Chrome Alum", "Chromopotassium Alum", or "Potassium Chromium Alum." Although synthesis is possible, it requires reducing Potassium Dichromate, which is highly toxic, carcinogenic, strongly oxidizing, and corrosive. In general, it poses significant safety risks. Therefore, it is much safer to buy Potassium Chromium(III) Disulfate Dodecahydrate ready-made.
Synthesis and Crystal Growth Procedure
Dissolve Potassium Chromium(III) Disulfate Dodecahydrate in the minimum possible amount of water. Important: dissolve the compound in water no warmer than room temperature. Heating produces a highly soluble modification that prevents proper crystallization. This step may require several days. Avoid adding excess water. If available, add a few drops of Sulfuric Acid to suppress hydrolysis and mold growth.
If increased transparency of the final crystals is desired, prepare a saturated Potassium Aluminium Disulfate Dodecahydrate solution and mix approximately 200 ml of it with 50 ml of the Potassium Chromium(III) Disulfate Dodecahydrate solution. Using a smaller proportion of Potassium Aluminium Disulfate Dodecahydrate will result in crystals that remain very dark.
Insert a fishing line into the solution and leave the system undisturbed until seed crystals begin to form. Once the crystals reach a suitable size, carefully remove the excess crystals so that only one or two remain attached to each line. Transfer the saturated solution into a clean vessel, collect any residual precipitate (which may be redissolved to produce additional solution), and place the fishing line with the selected crystals into the fresh solution to continue growth. Inspect the crystals periodically and remove new growths that form on the line to prevent undesirable fusion with the main crystal.
After approximately three weeks, large crystals will form. Detach the crystal from the fishing line with care. Potassium Chromium(III) Disulfate Dodecahydrate does not remain stable under normal atmospheric conditions; therefore, a protective coating (such as nail polish) is required. Alternatively, you can cover it with a stable isomorphic layer—for example, Potassium Aluminium Disulfate Dodecahydrate (place the crystal in a saturated solution of Potassium Aluminium Disulfate Dodecahydrate for several days until a protective layer forms).