Question

Generally why there is loss of weight of gold jewellery after being polished by gold smith

Answer 1

 whenever we give a gold ornament to a goldsmith for polish, he washes the ornament in the solution called aqua regia which is able to dissolve gold . so a thin layer of gold get dissolve in that solution and we find a shiny surface bcoz of the next layer. and only because a layer get dissolves in it, we find a difference in weight of the ornament.