Ed's Editorial

Gas/Propane Forges…. A Primer


  This article IS NOT intended to be all encompassing, it is primer, focusing on the differences between gas forges used my Bladesmtihs, and those used by General Blacksmtihs, with some “Do” and “Don’ts”, and safety thrown in for good measure!


As one who started my career as a Blacksmith, I agree that there is a world of difference between Blacksmithing and Bladesmithings, AND the equipment used for each.   The way/method that a Blacksmith’s forge heats is generally not a factor, because of the material/steel types utilized…… short of a forge “burning” the material/steel, there’s not much consideration as to how a Blacksmith’s forge heats.

Now, it’s a totally different story with Bladesmithing.   The materials/steels that Bladesmiths forge are usually VERY heat sensitive, and can be easily degraded with improper heating.   Evenness of heating can also make the difference between a successful or a failed outcome, particularly with Damascus/laminated steels.

So, those things being taken into consideration, the how’s and whys of a Blacksmithing forge are far less important than those of a Bladesmithing forge.

So, what should those seeking a Bladesmithing forge look for?  Based on my experiences, here goes….

  1. Round design period.  Even if the burner is not placed in the optimal location(s)/position(s), a round forge is always a better choice for Bladesmithing because there are far few “hot spots” than in any “square” design.   Flamepattern1
  2. Burner(s):  A SINGLE blown burner, of proper size is by far the least complicated, easiest to use/operate, and most versatile of any forge burner(s).blowerburner1.jpg

**What should you look for/build in a blown burner??

-Black iron pipe

-A blower SPECIFICALLY DESIGNED/BUILT FOR FORGE APPLICATIONS.  (NO “squirrel cage” blowers, because they they are design to operate where NO BACK PRESSURE is present, and WILL burn out at some point…usually sooner than later. ALWAYS PURCHASE A BLOWER THAT IS DESIGNED/BUILT FOR A FORGE APPLICATION.  Personally, I buy mine from Blacksmiths Depot online.


-Sizing:  It always better to err on the side of a burner and/or blower being too large….. You can always “dial it down” as required, but if a burner and/or blower are too small, and you open everything up to its max…..and still don’t get the heat level you need…… you’re only option is to buy/build a bigger burner and/or blower. So again…its better to have a burner/blower that is too large, versus one that is too small.

-Where the fuel enters the burner The further away from the ignition point, the better the fuel & air mix…. and if there is an angle built into the burner (such as a 90 degree elbow) all the better, provided the fuel inlet is positioned very close the end the blower is attached to.

-A propane needle valve at the fuel inlet which allows far more control than a typical ball valve.  (use a ball valve at/near the fuel source.  Ball valves are either FULLY OPEN OR FULLY CLOSED….. DO NOT try to use them for anything in between!! I always place a ball valve at the propane source….if a tank, then right after the regulator.  If you have a large outside tank, place the ball valve where the propane comes through the wall, etc, and into your shop.




NOTE:  Can you use venture or multiple burners??  SURE!!  But by doing so you inherit many potential issues/problems that do not occur with a single blown burner, I simply don’t understand why anyone would want to.  I have given up trying to help those who insist on using multiple burners, especially the venture type in a square forge design… my thought pattern with this is….. Some people are always trying to ice skate uphill. Do yourself a favor, and build a single blown type burner!  It will run trouble free for YEARS, and you can spend your time forging, versus messing around, trying to get venture burners to operate correctly.

Here’s an exert from a recent forum thread, where I was attempting to explain to an individual about venturi burners:

“I’m not going to attempt to answer the question about where to put the burners  (multiple venturi burners), simply because getting multiple venturi burners to work well/correctly, in the same forge is nearly impossible. To explain, I’ll concentrate on a two burner setup here…… when fed off the same fuel supply, one burner will always get more fuel than the other, meaning one burner will burn hotter than the other, and all the things that go along with that occur. I’ve seen people waste literally months and months of their time goofing/trying to adjust multi venturi burner forges, trying to adjust them……and they never can. Those who tell me they have a multi venturi burner forges that are “adjusted just fine”, are ones I don’t even bother trying to help, because they either have no clue, are are simply in denial. The ONLY time I would recommend a venturi burner, is for a single burner application, and then for someone who will never required “welding heat”, and/or who needs a forge that either requires no power, or must be portable. So how does one make a multi burner venturi setup work correctly? The only way I have ever seen it accomplished is to have completely separate/independent fuel systems to each burner, then each burner is adjust as if it were the only burner. Everybody has this fantasy that using a “T” to supply a single fuel line to two burners means they must be getting equal fuel…..and it’s just not true. The line to one burner might be a bit longer or shorter then the other, the ID might vary, or any of a hundred other things….but two venturi burners, running off the same fuel line never get the same amount of fuel.

I have no idea why so many beginners gravitate towards venturi burners….they are far more complicated, far more finicky to work with and adjust, and consume far more fuel than any blown style burner. Maybe it’s back to the “lemmings” jumping off a cliff?”


  1.  Refractory/Linings:  Basically you have two types to choose, Blanket/ceramic fiber, or castable.   There are others, but cost and availability usually put them out of reach for the average person.   Each refractory has its pro and cons, and each heats in a different manner.   Most believe that refractories are simply “reflectors”…..not so.  There is also a common belief that “more is better”, particularly when it comes to the blanket/ceramic fiber refractories…. which is also a fallacy.

Castable:   Very durable and long lasting.  It is intended to absorb a given amount of  heat, then start reflecting….the amount of heat absorbed/reflected differs for each variety…in general, those castable refractories with lower temp ratings will absorb more heat before reflecting, and tend to look heat quicker.   Those with higher temp ratings absorb less heat before they start refelecting, and tend to “hold” the heat longer.     Most varieties of castable work best in a layer of at least 3″. My personal favorite castable refractory is Cast-O-Lite 3000.

The issues with castable refractories are:

-VERY specific mixing ratios must be observed for product to perform as advertised.

-MUST be allow to cure NATURALLY to be durable.  “Firing” to force cure it GREATLY REDUCES THE REFRACTORY’S LIFESPAN.

-Significant amount of time required to heat a forge using this material….typically 45min-2 hours.

The Pros:

-The best durability of any forge lining material.

-Once heated, you can turn down the fuel/psi and the forge will maintain its heat

-Temp does not drop significantly when a large piece of steel/billet is inserted

-Does not give off dust/fiber during use like Blanket/ceramic fiber does.

-Overall forge will last for years, versus weeks of months Blanket/ceramic fiber….especially if flux is used.


Blanket/Ceramic Fiber: This material is also engineered to absorb a given amount of heat before it starts reflecting.  How much and how fast are dependent on the type/variety.  For the purpose of this information, I will ONLY CONSIDER 1” THICK X #8 DENSITY Blanket/Ceramic Fiber.   This is the place where I’ll lose some of you.  For anyone who is/intends to use 2” of more of #8 Ceramic Fiber for a forge….. You are wasting your money and costing yourself extra fuel every time you use the forge.

I’ve done the tests, using the exact same forge body, burner, etc.   1” of #8 density ceramic fiber reaches temp quicker, on less fuel pressure, and maintains that heat WHILE WORKING IN THE FORGE  at a lower fuel consumption than 2” of the same material…..weather that’s a single 2” layer….or 2, 1” layers stacked.

Next, Blanket/Ceramic Fiber SHOULD have some type of “coating” to keep the ceramic fibers from flying around and getting sucked into your lungs.   The best coating that I have ever found is ITC-100.   It’s expensive, but a pint will do SEVERAL coatings in a large sized forge is reduced properly.

VERY little of this product is necessary to gain the maximum benefit.  MORE IS NOT BETTER!!!  Use too much, and your just wasting the product, and in many cases, reducing its effectiveness.   How?  A couple of tablespoons in a paint/mixing cup…..add water and keep stirring until you get the consistency of latex paint (NO THICKER).  Spritz the inside of the forge (already lined with Blanket/Ceramic Fiber) with water/spray bottle.   Using a cheap paint brush, simply paint the coating onto the interior of the forge/lining.   One done as with all refractory products…. It must be allowed to cure naturally!   This is so important, that I feel it necessary to explain further… Many, because of impatience want to “fire” the forge to a given point, then shut it down, and let cool, then repeat.  THE ONLY THING BEING DONE IS A FURTHER WEAKENING/LIFE SPAN SHORTENING OF THE REFRACTORY……..simple as that.

    Now that I’ve beaten that dead horse some more, just how can you “expedite” curing the refractory??  AT MOST, place a single “heat lamp” bulb, or a 100 watt incandescent light bulb inside the forge, and LEAVE IT ALONE!!  Depending on where you live/the environment, it could be from a couple of week, to a couple of months for the refractory to cure.  One novel approach that a student of mine did….a couple days after “pouring” his new forge….he placed it atop a wood stove in his shop, that basically burned 24/7…. And within 2 weeks his forge was nicely cured, and ready to fire.

Even with a lengthy curing time for a castable refractory forge, care must still be taken on the initial “firing“….. I like to bring the forge to about 500F, then shut down and let cool overnight…..next day I will take it to 1000F, then shut down, and allow to cool COMPLETELY.  Next firing, it “let it go” time.  Usually a new castable refractory forge will get to around 1500-1700F and stall….meaning it won’t get hotter…for a while.  That “while” will entail a lot of steam and maybe even drops of water as the last remaining moisture is forced out.  Once the steaming and weeping end, the forge temp will start to climb again, and they treat it as normal…go to work, and have fun!!


   This is the part that everyone hates, but I’m going to lay it out plain as day for you….  YOU BUILD, SETUP, AND USE A PROPANE FORGE AT YOUR OWN RISK!!  I have seen so many people do really dumb things over the years, it’s ceased to surprise me.  Here are some tips that will make things as safe as possible…

-NEVER PLACE/USE A FORGE CLOSER THAN 6 FEET TO ANY FLAMMABLES!  THAT MEANS WALLS, DOORS, FLOORS, AND SOMETHING MOST NEVER CONSIDER CEILINGS!  This goes double for things that can melt….. These forges are heat throwing monsters, and I have seen items as far away as 8 feet from the front opening of a forge melt!

You also have to keep distance and safety in mind when building….

DO NOT build a cart for your forge, with a propane tank sitting on the bottom of the cart…..when I said AT LEAST 6 FEET…. And means your propane source too!  Also, electrical wires, and/or anything else that can melt should be kept as far from the forge as possible, or at the very least, heat shielded.  OK…ONE MORE thing…..hoses and fuel lines…. MAKE SURE THEY ARE RATE FOR GAS/PROPANE!!  There is a reason that they make PROPANE hose…..because if you try to use other hose, such as air hose, fuel hose, etc….. Propane will break down/eat up the hose from the inside out…..and if you forge is running when it lets go….You and your shop will be a smoking hole in the ground!!

Next, let’s talk about propane.  Propane is heavier than air. That means if a leak occurs, it will naturally “pool” at the lowest point(s) on a shop floor, and if a spark or other ignition source reaches it….not good.  So, how do we protect ourselves??  First, we regularly (I do it weekly) inspect ALL propane lines, pipes, tanks, hoses, regulators, valves, and any connections visually, to ensure they are good and not damaged in any way.  I also go over EVERY connection with a spray bottle of soapy water….you see even the tiniest bubble(s)…you have a leak….FIX IT!!

One final rule for all forges with a blower type burner….. THE BLOWER IS ALWAYS THE FIRST THING TURNED ON…..AND IT IS THAT LAST THING TURNED OFF Follow that rule and you will eliminate 90% of possible accidents.

I could go on and on forever with various scenarios of do’s and don’ts for propane forges, and never cover it all.    A propane forge is nothing more than a controlled explosion.  Keep that in mind at all times, and your mind will be in the right place.  Don’t HOB KNOB anything when it comes to a forge….your life is literally at stake if you do.


(My current welding forge, after removing the forms and before allowing it to cure (this one took almost 2 months to cure before it’s first firing)

But once cured and in use……..




Good Luck!!


Ed Caffrey, ABS Mastersmith

“The Montana Bladesmith” 

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