A sample taken from champion Black Caviar after her 2011 TJ Smith Stakes win has been cleared for cobalt.

Racing NSW stewards took the unusual step of publicising the result of the retrospective test to halt speculation the mare had raced with the controversial substance in her system.

Black Caviar's trainer Peter Moody is one of four Victorians involved in an investigation over illegal cobalt levels in horses in their care.

Moody has previously asked for all Black Caviar's samples to be tested to protect her reputation.

"We have had calls about Black Caviar so we decided to make it public," chief steward Ray Murrihy said.

"We have a lot of stored samples from a lot of horses that are being retested."

A cobalt threshold of 200mcg/L was introduced in Victoria last year and adopted nationally in January.

Newcastle trainer Darren Smith has been found guilty of more than 40 charges relating to cobalt from samples taken before the threshold was introduced in NSW.

Stewards determined cobalt to be a prohibited substance because it had the capacity to alter a horse's blood picture.

Smith admitted injecting horses with a substance obtained from a disqualified harness racing trainer who described it as a blood booster.

He will learn his penalty on Friday.