"Gold" Thompson Darby & Mattatuck Handcuffs

So this interesting auction only went for $59.99 after 1 bid, but these Darby handcuffs are actually very rare. I imagine part of the lack of interest, aside from the absence of keys for either pair, is that somewhere along the line, someone, for some reason, turned both of these handcuffs golden color. I'm not sure how it was done, as it doesn't really look like paint. Some sort of chemical bath? They certainly don't look BAD, and I thought it was just the camera/light but the seller did note that these have a gold finish. 
 

Above, the Thompson makers mark stamp

Below the makers mark for the Mattatucks 

Below, close up detail of the Darby locking mechanism. The bow of the shackle enters here, pressing the spring loaded inner portion downward due to the sloped locking tab. Once snapped shut, the internal spring holds the inner portion upward, and thus, the locking tab securely in the slot of the shackles end, until the internally threaded key is wound down onto the threaded bolt at the keyhole end of the locking tube, thereby compressing the internal spring and pulling back the locking tab to release the shackle.