Actually, a platinum ring will not necessarily read low (aka "be a low conductor") is the ring is big enough. This ring (of this post) is a man's ring, not a women's ring. Men's rings/bands are typically bigger, right? So just like yellow or white gold (which, as you know, alloyed gold is also a "low conductor", albeit not as low as platinum, size-per-size), the size of the ring plays into it. For example: a ring (whether platinum or gold) that is very small/dainty, will read down low, even down in to the foil range, right? Yet a husky fat band (whether platinum or gold) will read higher, up in to the round or even square tab range, right? Thus this rule of thumb (to account for size) is true not only of gold, but also of platinum.
Therefore, if you *really* want to get serious, take that bounty hunter rental machine to a jewelry store, and ask a kind-hearted jeweler to allow you to air-test sample a similar size/weight platinum band. Make mental note of where it lands on the conductive scale (I'm assuming your BH machine has a tiered or #'d TID scale on it, and isn't the basic beginner model with no other controls, graphs, scales, meters?). Then merely go to your yard, and concentrate on items that fall around those #'s.
Or as was already suggested, just dig everything that beeps (iron excepted, of course, to save time).
A possible problem you will encounter is that if your yard is filled with debri and small nick-knacks (foil, can slaw from decades gone-by, etc..., nails, etc...) that you will have reams of targets to sort through. The average un-initiated person is often surprised to find out *just* how much cr*p can accumulate into the average back yard of a house, that is only a few decades old (muchless 50 or 100 yr. old houses!). And remember: if your ring landed next to other metal object (like next to a tin sided tool shed, or next to a crushed soda can hidden just under the surface, or ..... whatever ..... that your object will be "masked" by the item it's lying next to or on top of. In other words: the TID's are only accurate for naked targets tested individually. Experience, of course, will help you ferret our and tell items apart, even in close proximety (or recognize signals which appear to be more than one munched together too close to get separate TID's). But to the uninitiated, it will just be senseless noise.
For example: I once went out and hunted for a buried cannister of silver coins, that an elderly man had buried in his yard. After his death, his next of kin went looking for it, with a rented detector, with no success. It took me just 5 minutes to find it: He had buried it along-side the wall of the house, which had skewed the signal. The persons renting the machine just couldn't tell the difference between the obvious signal the house was giving (chicken mesh screen within the plaster of the house wall) and the signal of the silver coin cache there. But for me, I could tell that there was a momentary higher concentration of signal at *just* one spot along the length of the wall. Don't get lost in the example, because that's just one minor example, but ..... you get the picture.
