I have a brooch that I am pretty sure is gold. Stamped on the back is what looks like 1/2010 KG.R. I am not familiar with this type of marking but the brooch is an old brooch/pendant of an unusual shape so I was wondering what these markings actually mean?

1/2010 KG.R means nothing in the jewellery business pertaining to gold. In any language, in any country, gold is signified by the K weight sign, either l0, or l8. Sorry, not gold, could be an alloy looking like gold. Take it to a jeweller and have him assess.

More than likely "one twentieth (of) 10K" The term "RGP", meaning "rolled gold plate" is very common, or perhaps the "R" on the end is an "F", which would be "one twentieth (of) 10K gold-filled".