There are "Jiffy Marker" products that might "get you by" - The best for your purpose would be the "oil" version - sounds like a rattle inside and the black that comes out is very solid glossy black. Next best might be the "Industrial Super Permanent Ink" - I have some of these in the "Fine Point". Again much darker and blacker than the standard jiffy markers, which to my old eyes tend to dry with a blue black tinge to it. If there is a home-brew way of doing black adonizing on aluminum, I too would be interested to hear how to do that. Does not make for a "perfect" fix, but I have laid on fine layers onto scratches on scope bases - the marker paint has a thickness, and several careful coats can build up to fill the scratch, and the colour is not far from the adonize - but almost always can still be seen in the right light.