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I Forge Iron

Scale/Finish Problem

Pat Masterson

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Hey guys- so I’ve posted about this one before but I’m revisiting with more detail because I must be doing something wrong. Everything I’m making but especially the smaller stock stuff (3/16,1/4,3/8) has this terrible coating of very thin scale. I have a good butcher block and I’m going after the scale as hard as I can but it’s still there when it cools. Maybe the finish in the pictures looks ok but if I were to drop one of these pieces on the driveway for example, a little piece here and there would chip off. And you can see they are not smooth at all. So before I put a paste wax finish on I’m having to file/sand almost the entire piece to bare metal, then bring it to a black heat and at that point apply the paste wax. Seems like anytime I watch a video they forge, wire brush a bit but not excessively and then just do some minor file work depending on the piece before doing the finish. Am I doing something wrong? The picture with a bunch is right after they cooled. The second with just two pieces shows what I’m having to do to them before putting the finish on. I really appreciate any help. 



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If you want to get to bare metal you will have to A work in a hard vacuum, B power wire brush---tedious and DANGEROUS, C sand blast, D tumble or E chemically remove it.

We can't coach you on how to tune your forge to help as you don't include any details of what you are using.  Sort of like asking car engine help without telling us if it's gas or diesel...

Most forged items I do do not get taken down to bare metal; a good wire brushing as it goes from glowing to black suffices for me and makes getting a nice dark surface finish to it.  My icicles that are supposed to be silver I wire brushed on a slow speed motorized wire brush---and then spray painted silver!

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I meant to mention the forge set up, sorry..it’s from Devil Forge - the smallest one they make with one burner. The forge confuses me to be honest..i thought the higher the gas pressure the hotter the flame but that doesn’t seem to be the case. It seems to get its hottest running between .1 and .2 mpa with the choke open a little more than half an inch...could the choke being too far open affect the scale or should I be able to take care of it by brushing at the right heat regardless? Like I said there’s a definite sweet spot for the choke/gas pressure setting regarding the way the burner runs..it will sputter a bit if it doesn’t like the way it’s set up. Should I try to find a setting that doesn’t cause the sputtering but has the choke closed more? 

In the end I’m able to get a nice finish after filing, bringing it to a really low heat and then applying the paste wax but I just feel like I should be getting there much easier. 


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Yes the choke has a MASSIVE effect on scale production.  An oxidizing flame causes heavy scale production, a neutral to reducing flame creates much lower amounts of scale. Not placing the workpiece in the direct flame can help as the oxygen may not be totally consumed as the flame exits the burner.


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Yes and depending on how your burner is made it may need the choke adjusted for every different psi and even hot vs cold forge.  I tuned by ear and eye for about 20 years; not a big task.  Set the pressure, tune with the choke for the burn wanted. Adjust after the forge heats up.  If I adjust the pressure I adjust the choke as well.

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  • 1 month later...

All the important things about unsing the forge to minimize the scale have already been said.

But if it is too late to lock the stable door after the horse has bolted(hope that I´m using this aphorism in the right manner :) ), I like to give you an idea how to "rescue" these pieces...

Chemical scale removement may help you:

white vinigar works fine. I´m using normal 10%white vinigar from a normal food store near to my location. Stored in a plastic barrel. Leaving the pieces in there overnight is just enouh, even for heavy scale. In most cases you can wipe of the rest of the scale simply by hand/toothbrush under running water.

Maybe you won´t like the bright silver shiny surfaces you will get with this method?

Another drawback maybe that you have hurry up a little bit to make your pieces dry after cleaning under water, because rust will come up in minutes, even if you have dried everthing carefully, there is no much time befor it will get a thin rusty coating. So if you want to try it out it is recomandated to dry things good after cleaning with water and make your coating (paste wax ect...) immediately afterwards.

If you indeed don´t like this silvery look, go back to the forge and heat the pieces up to a dark red heat for rescaling to your liking. If you take the pieces out of the forge start wirebrushing until it is cool and you should end up with a nice, more blacksmithing like colour....


Greetings Sascha

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