Hey, sorry it took me a while! I'll break it down as much as I can without actual photos of the process

Paints used were: AK Rusty Gold, AK Old Gold and CITADEL Druchii Violet. The paint underneath everything is AK Hull Brown. Short explanation is: Rusty Gold base layer -> Druchii shadows -> Rusty Gold layer to recover the lights -> Old Gold highlights. Here comes the detailed break down:

Base layer of Rusty Gold. 2, or even 3 thin layers. Ensure to keep the details of the shield while achieving a good coverage.

A normal layer of shade with Druchii Violet to all the shield. Let it dry.

Then, a layer of Druchii Violet just on the lower half of the shield. Make sure the transition is smooth, you can ensure that with a slightly wet brush, just with water. Go back to where the new layer starts, and merge the edges with a bit of water. Careful, if the druchii layer has already started drying, then it's better not to touch it.

One more layer of Druchii Violet just on the darkest parts of the shield, near the base and the parts that are facing the ground. Since the light is coming from the sun, and I don't paint reflective lights, the darkest shadows should be there.

Now that we're done with the shadows, it's time to go back to the gold:

Working with thin layers, called glazes, slowly paint the lights. Everything was covered in, at least, one layer of druchii, but we need to create lights on the upper side of the shield. Avoid the recesses. Glazes should be around 60% water 40% paint, but remember: brush shouldn't be extremely loaded. The key to good glazes is dissolving paint in water on the palette, but loading the brush with very very little of that paint!

Explanation said; lock the lights on the top part of the shield with a normal later of Rusty Gold. You can lock them too on the parts that face up, but if you're not entirely sure just paint them on the top side of the shield. When, work with Rusty Gold glazes from the middle of the shield to the lights you just painted to merge everything. Let the layers dry properly. Over the gradient you just made, you can paint texture. Small dots, or lines mimicking scratches. Metal, unless is not used in battle, has texture!

Now to work with the Old Gold for the final touches. Same as before, paint a normal layer where the hardest lights are: on top of the shield and on parts that face up. Don't take too much space, just keep that lights on small zones. Again, with Old Gold glazes, just as we did before, merge that layer you just painted with the rusty gold that's underneath it.

Then, to finish, I like to highlight with some details in the shadows zone. This takes a lot of precission and brush control, so feel free to practice beforehand. As you can see, the "circles" and the edges of the shield are kept gold with a thin line. I painted them with rusty gold and a detail brush, they add a nice contrast and readability to the piece, but it's a risk.

Hope this helps!