✅ SOLVED Patent Plate?

Knight_of_Excalibur_II · Jan 21, 2026

A while back, I found an iron plate, heavily encrusted. I've tried to clean it, but some of the encrustation is really stubborn. On the plate I could make out "PAT NO 2.....5", a friend recommended that this is a patent plate. What do you think? If it is, can you narrow down the potential patent? Found this in the dry sand beach metal detecting in Jupiter, FL. Any info you can provide is very much appreciated!

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cudamark · Jan 22, 2026

Lots of older items had patent dates cast or stamped into them....from buckles to stoves and beyond. Without an I.D. on the item, or, a full patent number and date, it will be difficult to tell exactly what it came of off.

Knight_of_Excalibur_II · Jan 22, 2026

cudamark said:
Lots of older items had patent dates cast or stamped into them....from buckles to stoves and beyond. Without an I.D. on the item, or, a full patent number and date, it will be difficult to tell exactly what it came of off.

I'm cleaning it with the current solutions I have at hand, but they are too weak / slow; I'm going to order stronger stuff tomorrow or this weekend. I can see the vague outline of the next two digits, but there's too much crust in between them to discern what they are for now. Will post updates once it's more distinctive.

cudamark · Jan 22, 2026

Try Evaporust or electrolysis.

Knight_of_Excalibur_II · Jan 24, 2026

Store was out of stock of Evaporust, but I found a product they advertised as being of similar strength called "Rust Aid". Buying some gear for electrolysis as well. Let the plate soak for ~1 day in Rust Aid, here is the current progress:

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Can make out "PAT NO 27....15" now, 2 more digits. 2 or 3 more left to go, the encrustation in the middle is super stubborn though, and I'd like to avoid scratching it if possible.