Hey guys, meant to upload this right after the stream, but Here's a quick and dirty tutorial of how I shade metal, which you might find helpful.
This can be done in any program that gives you access to a round blend-able brush. It also includes the value swatches I regularly use in my metal painting.
For the shown example, i use a basic round SAI brush, 25-50% blending.
1.) Start by defining your base shape. You'll be refining this over the course of the process. You can also choose to create a lineart of the shape and shade it using the same values.
2.) Begin establishing the initial gradients for your metal, and place the black contrast regions. USE A REFERENCE! (seriously, I can't stress this enough. Using metallic references will save your butt.) These contrast regions will begin defining the geometry of the shape, and will help you make adjustments to it as you paint. Note how my painted object is shaped throughout the steps.
3.) begin defining more complex contours using a combination of darker and lighter colors, adding pure white to the specular highlights.
4.) begin using more white to define reflections and shapes.
5.) (optional) I personally like to break up uniform planes with surface reflections, particularly using more black and white. It depends on the object you're painting.
6.) At this point I also begin to tint the black regions with the ambient light color. Personally, I use complimentary colors for my highlight and shadows, so In this example, I tint the darker regions with blue.
7.) Now i begin blending the metal into the rest of the composition, creating cast shadows, highlight zones, etc.
8.) HIGHLIGHTS. for this step I use Sai's Luminosity layerstate, but if you have Photoshop, the equivalent layer state is going to be Linear Dodge.
I first use a clipping mask with the color of my point source light (in this case orange) and paint over the lightest regions of the metal. I also create a nonclipped layer with the same blending states (luminosity) and lightly airbrush blooms in with the same color.
It all depends on the object and the type of metal you're shading, but this is my angle of approach. For brass/gold, simply use the respective metal colors instead of grey tones.