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I Forge Iron

Rust and hot spots inside forge


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I am new to this forum but been smithing for 5 years. 
My gas forge has a few hot spots that show up during the initial light but then fade away once I’m up to heat. I have not had this happen before and I have just re-lined my propane forge. Also I have some odd looking rust spots that showed up this morning after working last night on the liner. Any ideas on what could cause that? Thank you in advance! 


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Burning propane gas produces many by-product gases.

One of them is water vapor. A great amount of it is given off every session.

Try to put on a top coat of water resistant, (proof?) material.

The outer coat should cover the rust stains. If you must get rid of the rust stain,

oxalic acid will get rid of, (react with), the rust. Please note that that acid is toxic, when ingested. So store it in a safe dry place.

Other acids will work.

Such as,

citric,  phosphoric,  (even tannic), acetic (vinegar), and mild hydrochloric acid.

Vinegar is your best bet. But it is slow.

Flush the acid and dry thoroughly before applying the coating.

Hope that helps,


2021 is soon to come. Ya'll, have a great year!



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I used hellcote on mine too...

Another thing you'll notice is that when your propane tank gets low, or starts freezing- i get a dark spot in mine right where the forced air burner hits the other wall of my forge. It literally turns black/brown. Only happens when the tank runs low on pressure. 

My guess is that a little of the liquid propane is picked up and blowing thru my burner... or moisture. Not really sure, or if there's a term for it.

Next time firing up the forge- it goes away under fresh heat. No structural impact i can tell or see from it.

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