I'm building a couple industrial style tables, using black pipe from Home Depot for the legs. The fittings and smaller nipples are all a faded gray color that perfectly complements the black cherry stain I used on the wood. But the longer segments of pipe come in a black color that is too dark and very patchy and uneven. I would really like to remove it and ideally match the color of the fittings.
Based on some research, I tried using mineral spirits to clean them up. This had very little effect. Next I tried sanding. This does break through the black, but is very slow going and the sand paper quickly fills up with black goop. Also this cuts all the way through to the underlying metal, which results in a shinier color than the fittings. There's got to be a better way.
According to this video, the black stuff is mill scale and can be removed with Jasco paint and epoxy remover. This does look effective from the clip, but the Jasco stuff is $45/gal and seems pretty toxic. Also I'm skeptical that the black stuff is actually mill scale.
Before I drop the money on the Jasco, can anyone tell me what the stuff is and maybe recommend a less toxic way of removing it? I wouldn't mind painting over it if I can figure out how to properly prime the current surface so the paint stays on.
Best Answer
It is "mill varnish" , nothing to do with mill scale. I find no definition in the ASTM index. Very likely it is a varnish ; A resin plus a solvent/vehicle. Mineral spirits or gasoline should take it off. Different mills may use different products as there is no firm definition. It is applied to new , relatively scale free pipe. A industrial purchaser does not want to see his brand new pipe delivery covered with rust. Oil companies sometime order pipe with no mill varnish as it is a nuisance to remove. I have seen it hard like paint , I have seen is still gooey. Mill scale is thick black iron oxide scale; Fe O and Fe3 O4. The mill removes scale with concentrated sulfuric acid. I have seen some new steel products with scale allowed to weather , rust ( complex hydrated Fe3 O4 - brown) will loosed the mill scale so blast cleaning is easier