erythrosine

noun

eryth·​ro·​sine i-ˈrith-rə-sən  -ˌsēn 

variants also erythrosin

-sən 

: a brick-red powdered xanthene dye C₂₀H₆I₄Na₂O₅ that is used as a biological stain and in dentistry as an agent to disclose plaque on teeth

called also erythrosine sodium