Thanks Kevin! There are 2 products out in the market that I use for slight weathering. It's a pretty simple process, I don't consider myself to be a professional when it comes to weathering but I have learned some basics that have helped me along the way.
What I did was purchase a wash that is sold at the Games Workshop stores, these are the strategy fantasy gaming stores that sell those little Warhammer figures. They have an assortment of little things that are pretty useful to us modellers if you take a closer look when visiting one of these stores.
I like to buy their washes, they come in a variety of colors but I always choose the Badab Black wash.
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After painting the engine with Testor's Metallizer paints, I liberally apply the wash to the whole engine with a small brush. The wash settles in the low spots and ultimately gives the engine a more dimensional and detailed look. Don't be shy when applying it, it is very thin. After this step I apply a product sold at Michael's called Rub 'n Buff. It is a pastelike metallic finish that also comes in various shades, in this case, Silver Leaf. A small dab on the finger goes a very long way so you have to use it sparingly. What I like to do, after placing a small amount on my index finger is rub off some of it on my other hand, this way it's easier to monitor the amount to be applied on the part.
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Ultimately, by doing this, you will be highlighting the raised or high spots on the part, this will give it a nice contrast against the previously applied wash.