From Goddards own site:
How Silver Dip Works:
1. Chemical Reaction:
As tarnished silver jewellery is immersed in a silver dip solution, a chemical reaction occurs. Thiourea or potassium thiocyanate in the solution reacts with the silver sulphide, which is broken down into one component, silver, and one component, sulphur.
2. Dissolving tarnish:
The silver sulphide dissolves into the solution as the chemical reaction proceeds, leaving behind a transparent, untarnished silver sheet. During this process, the tarnishing process is reversed, revealing the shiny silver surface underneath.
No mention of 'etching'?