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I Forge Iron

Help with scale

Pat Masterson

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Hi everyone. Brand new here so I hope I’m posting in the right place. 2 pieces into blacksmithing- an icicle tree ornament and dice bottle opener. I’m having the same issue with both though. The bottle opener especially has a lot of scale. I brushed it as hard as I could when it was hot (may need a better brush as I just have a Home Depot brush) but I put a paste wax finish on it and now a lot scale is chipping off very easily. Can I put it back in the forge to a very low heat and brush some more? Can I file it and then into the forge to a very low heat? Will that bring the dark finish back after filing? Do I need to remove the paste wax with turpentine or something before heating? Any help is much appreciated!! Thanks. 

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Welcome aboard Pat, glad to have you. If you put your general location in the header you'll have a much better chance of hooking up with members within visiting distance. 

If you're using a wire brush you're going to have to go to a LOT of effort cleaning the scale. A flat bristle "butcher block" brush is much more effective. 

If you're VERY CAREFUL!!! you can use a cup brush in a disk grinder. Or a wire wheel on a bench grinder. Be aware though powered wire brushes are extremely dangerous, one misstep and it will grab the work out of your hands and throw it at high velocity. IF you're LUCKY, if you aren't the wheel will pull YOU in and strip flesh and break bones, possibly removing fingers. 

A good vice, serious PPE and a careful light touch makes a cup brush reasonably safe. I use them regularly but I also pick wires out of my hands and sometimes arms and I wear a leather jacket using one. It's also almost the only time I wear my blacksmith apron. Safety glasses, goggles are better under a full face shield. 

I'm not trying to scare you. . . well not more than the tool deserves but they are really dangerous. Check with a butcher supply but they are available at blacksmith supplies though a bit more spendy. They take decades to wear out though.

However, once you get to making lots of small items like your first two a tumbler is an excellent method of descaling and readying for finishing, wax, oil or paint.

Frosty The Lucky.

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To add to what Thomas said, rewax with the piece warm. Like hot but not too hot that it's burning the wax. 

Or, on some pieces, I like to use spray can engine or exhaust clearcoat. Matt, flat or low gloss are preferred since it doesn't look shiny. These clearcoats are more expensive but I've found them to hold up better than other spray can clears, and they dry faster.  They can be found at lots of chain store auto parts stores. 

I usually apply these after wire wheeling or after the piece is cleaned by wire brushing from the forge. 

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Great tips for cleaning off scale. Good job.

One other reason for maintaining a substantially clean anvil surface is,  that scale, (iron oxide) is that that  scale particles are way harder than than the iron or steel that we are hammering.

Particles of scale can end up in the metal being forging. It can cause problems in the forged steel.  And it's a swine to get out.


(fellow iron bangers).


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On 10/23/2020 at 7:13 PM, Pat Masterson said:

back in the forge

What type of forge? If it's a coal or charcoal fuel you may be putting the stock into the oxidizing portion of the fire, causing it to scale up too much. Once I learned fire maintenance in the coal forge, I have much less scale forming on the stock. Another problem is too much air for the size of the stock. If you are using propane your burner may be running too lean causing scale.

Have you seen this yet?




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The best advice I can give for scale is to remember that the first number is units in your drawing and the second number is units in the original. Thus, something that is 1" in your drawing is 3" on the original, if the scale is 1:3.

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  • 3 weeks later...
On 10/23/2020 at 11:00 PM, ThomasPowers said:

Burn off the wax in the forge.  Immerse the items in household vinegar over night, wire brush by hand under running water in the morning.  Neutralize vinegar and rewax.


I'll have to try this approach sometime.

My approach would be to burn off wax in forge, then go in manually with files/sandpaper to work the thick scale off to a semi-finished state. Then put back into forge to build up just a thin layer of uniform scale and refinish with wax.

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  • 2 weeks later...

Hey guys.. I have a follow up here - so I got a better brush, a butcher block from blacksmith depot, and it’s a huge difference. But I’m planning to make a couple things from a piece of 1/8” A36 plate I bought. I threw some cut off pieces in the forge the other day to test a touch mark I made and the scale on the plate was just crazy...like I had never seen before (in my very long 6 months of blacksmithing lol) but still it surprised me. It seemed like it was scale on top of scale straight from the forge without even getting to the anvil. This was my first time with anything other than round or square bar so does plate just act differently? I was under the impression the bar stock I was using was A36 also so that’s why I bought the specific plate I bought. Can the way I have this small propane forge set up be causing more scale than it should?

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Two things:

First, an oxidizing flame in the forge will encourage scale formation. See the Forges section of the forum for info on how to diagnose and fix this. 

Second, new steel almost always has a layer of mill scale on it from being rolled to shape, so the first time you put it in the fire, that layer will flake off as well.

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