I don't deny the mark exists. I don't deny that a ring with that mark may contain some variable content of gold - or not.
I'll repeat my statement:
"Solid Gold" is not a mark of purity in any country.
The fact that it is marked by the word "Gold" means it may have some gold content. If it was manufactured or sold in the United States it would have had to be manufactured before 1906. That might help in dating it IF it does contain gold. In the U.S. after 1906 it was unlawful to use the word "gold" when marking jewelry unless you stated the purity. In addition the lowest karat allowed for items sold in the United States is and has been 10k for more than 100 years. That was already covered by Red-Coat in his earlier informative post in this thread.
Without an assurance of purity, whether legal or not, the only reason to consider that an item marked "solid gold" actually has a gold content is to melt it down and assay the result. Anything else is hubris. I can say this with some authority because in the 1970's I purchased a lot of these early "gold" items and my experience was that about 20% of the items contained no gold whatsoever and the remainder seldom exceeded 25% gold (6k).
Refiners know all about these marks and the lack of any purity standard. That's probably why they all have this statement somewhere in their documentation. "10 karat is the minimum recognized purity of an alloy to be called "gold" in the United States."
