Re gain mill finish

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Hi everyone.I'm working on a steel/wood coffee table and need some advise. The table frame is made from 1-1/2" square steel tube and welded together. I want to keep the mill finish and clear coat but where I welded and ground the difference in finish is quite drastic. Any thoughts as to try to match? Chemical etch of some kind or heat/oil process???Thanks in advance.
Reply:Hi, i'm making a set of stair rails and had the exact same question.  Did you get a response or did you figure out how to preserve the mill finish after grinding down the welds?
Reply:Hi, first of all you must understand what mill finish is....it's the oxidised steel surface that has been rolled flat as the steel is produced.I have produced this finish inadvertently when heating a piece of clean, without scale, steel bar for a bending job, using a heat source that made the steel red hot for bending, but the finish is scaly due to the fact that it is not rolled flat like sheet steel in the rolling mill.If you just heated the steel area that has been ground clean you would get a definite colour mismatch, even though the steel will turn blue at about 600 deg C which is the temperature for tempering springs etc, due to you not having the thick scale that you get from blistering heat and rolling forces.My suggestion would be to lightly with 240 grit paper on a disc sander completely clean the surface and then go in with an Oxy/Acc burner and get the plate reaslly hot so that the surface discolours to the blue black and then clear coat it afterwards....you will probably use tons of Oxy/Acc and also risk distortion from the uneven heating.You could lightly abrade the surface to get an even finish and then apply gun blue and then clear coat.I have in the past used the oil blacking process where you first clean the scale off the steel to a bright finish and then by dipping and heating the steel produce an oil blacked finish progressively.....Propane was the means of heating.....you can get quite a dark almost black finish, something like the black you get on a frying pan from the cooking oil that bakes onto the outside of it.Don't get the steel to red heat or you'll burn the oil off, about 200 to 300 deg C should do it......most oven cooking is done at 200 deg C and stainless steel cook pans are very difficult to clean off once they have been used a number of times and not properly had the burned on cooking oil cleaned off.You might find that vegetable cooking oil is the best oil blacking medium as it breaks down at a lower temperature than old motor oil.BTW, I have many oil blacked machine items that were done 40 years ago and are still with a black coating.Ian.Last edited by puddytat; 10-31-2012 at 12:02 PM.
Reply:Look on some knife making forums, they have lots of easy finishes that they use on blades. I had luck with vinegar in the past, but we use alot of black patina from sur fin chemical. It is not the same as millscale, but it is a nice dark black with a natural look to it. You can clear coat over it or wax or wd-40.