I'm not sure how to go about 'gold dipping' a gemstone/geode slice. I'm not sure whether the term gold dipping is a misnomer as I for one would not like to dip a mineral into molten gold!
But here's an idea, I have a pen plating kit for gold plating and it is perfect for small applications and I'm sure you could use it on gemstones too, providing you buy the extra electrophoretic lacquer that allows to to plate none metallic items. You'd have to selectively apply the lacquer to the rim or surface of the gemstone that you want to plate, allow to dry for a suitable amount of time and then use the pen plating kit with gold plating solution to carefully plate the selected area. Plating is not difficult to do and you can buy full pen plating kits for around $100. The gold solution lasts for ages and if you buy a pen plating kit you'll be able to plate your sterling silver to create vermeil (although, you can only call it vermeil if you know the exact amount of gold applied, it has to be over 2.5 microns I think). Even so, you can make lovely gold plated silver. You can also buy different plating solutions so you can do rose gold, silver, rhodium plating, etc.
:)
