This technique came about as a result of a class I was teaching - a participant asked me how was it possible to create an effect which made the object look like fluid chrome or quicksilver. After some discussion, it emerged that he had seen a YouTube tutorial that was more bragging than teach; no surprise there as most of YouTube's so-called "tutorials" are like that. Most either gloss over the steps, move the mouse in endless circles around the screen or click things so quickly you have no idea what was clicked, or display dialog boxes so minuscule that settings are impossible to determine.
So here's my version of the technique and its surprisingly easy using Adjustment Layers!
Begin with the intended image.
For this example I decided to make some apples into modern-day Hesperides (FYI: the Hesperides were golden apples given to Zeus by his wife Hera as a wedding gift. They were guarded in a secret garden by a 100-headed dragon named Ladon and also by the Hesperides, the nymph-daughters of Atlas, from which comes the name. Obtaining the apples was one of the 12 Labours of Hercules.)
You can download the exact apple image I used from Pixabay (https://pixabay.com/en/apple-fruit-green-healthy-fresh-662003/)
Start the transformation by rendering the image as a grayscale.
The quickest way to do that is use the Gradient Map Adjustment.
Just ensure your Foreground/Background colour are at their default.
Once the image is black and white, you can add the Curves adjustment to make the apples look like they were formed of liquid metal.
The trick to this look is to "solarize" the Curve - add points and drag the Curve properties so it resembles the one shown below.
When you are satisfied with the "liquid metal" look, add a Hue/Saturation adjustment layer to turn the apples into their golden namesake.
Click the Colorize checkbox, and set the Hue and Saturation values to turn the apples a deep burnished gold. Here we are using Hue=45 and Saturation=49.
And there you have it!
The best part of this is that, because they are all Adjustment Layers, the effect is non-destructive and can be altered at any time.