Mosten acid

Mosten acid (PROSE: The Twin Dilemma) was an orange liquid (TV: The Twin Dilemma) which was invented by the Senilians to artificially age forged antiquities. It got its name from Professor Vinny Mosten, who exposed the ploy and was killed when a flask broke in his pocket, ageing him to death in seconds. (PROSE: The Twin Dilemma)

The Sixth Doctor found bottles of the acid in a laboratory in Azmael's palace on Jaconda and took them to use against Mestor. Whilst his first attempt to throw a bottle at Mestor was thwarted by a shield, he was able to kill him when Mestor entered Azmael's mind, which had the effect of shutting down the shield. The acid destroyed Mestor's body, meaning that his mind could not return to it when Azmael forced an attempted thirteenth regneration. (TV: The Twin Dilemma)