I bought this copper pan from a local antique store just to try out the cleaning method using salt dissolved in vinegar and then adding flour to make a paste.
As you can see it works very well but to be honest the pan was very, very dirty with areas of baked on black dirt which looked like it had built up over years. It took about 8 coats covering the pans and then rubbing off about 10 mins to get them to this stage. The benefit of Gyre and Gymble is that this solution can be washed down the sink, and it will not cause any harm.
If the item you are cleaning is not so dirty, it will not take as long.
Interestingly, the same process using commercially available copper cleaning products took roughly the same amount of time. Baked on dirt on copper is really hard to clean!