It is preferable to simply use a damp soft cloth or a soft bristle toothbrush to clean the gemstones and spinel jewellery.
Colour, carat weight, clarity and origin all play a role in how spinels are valued and collected. Gems whose provenance can be ascertained always have collectors. Red spinels that are deep red, large and relatively free of inclusions are also highly desired. So too are rare, deep blue spinels, particularly when a gemological laboratory has determined that cobalt is the colouring agent. Locality is playing an important role for collectors as well. Rare spinels from the Pamir Mountains are collectible, as are spinels from Burma. New localities that produce desirable colour – anywhere from pink to deep red are collectible.
Spinels are rarely treated, though occasional experimental heating of spinel has been reported
Spinels with surface reaching fissures are infrequently treated with oils or polymers
Most common: red, pink, orange, blue, violet, purple
Others are: brown, black
Rarely: yellow and colorless
Color change: greysh blue in daylight to purple in incandescent light
Due to the octahedral nature of spinel rough, the most common shape seen is the cushion
Rounds are also seen, as are other shapes, such as the emerald cut
In terms of clarity, spinel is often cleaner than ruby
The very finest reds are so rare that some clarity defect is almost always present (usually fractures)
Included crystals are quite common in spinel. Many stones display natural iron-oxide stains in their fractures