Alright I have been using plain old borax for welding and have had a few successful fluxes welds. I have read quite a few threads about fluxes and I'm going to make my own. I've read about iron powder, iron dioxide, boric acid, and just about everything else. Now what I've figured out through a lot of research is that carbon really does lower welding temps. So I plan on taking some old window weights I have that are cast iron and I'm going to get to work on filing them and collecting all the filings in a bucket then I'm going to take plain old borax and bake it at 350 for an hour to dehydrate it. And I'm going to mix 60% dehydrated borax 30% cast iron filings and 10% boric acid. Does this sound like a good mix?

Note: I will keep the mix in my welding rod oven to prevent it from rehydrating!

how is cast iron going to help in forge welding?

It's supposed to bring a little more carbon to the party and in turn lowers welding temps.

A much better way to make anhydrous borax is to melt it and grind up the resulting glass. IFI member (and general magician) jlpservicesinc has a useful video about what this looks like:

 

Nice. Thank you. That makes perfect sense. It wouldn't rehydrate that way correct?

Jennifer just keeps the ground-up anhydrous in a cookie tin, and it does fine. I've done the same, and can report similar results. The BIG difference is that the anhydrous does NOT foam up when you put it on the hot steel the way regular borax does straight from the box.

Another thing to think about (if you're interested in adding carbon to the mix) is the "Alaska flux" recipe from IFI member teenylittlemetalguy, announced in this comment and discussed in the subsequent comments:

 

The extra carbon is also an oxygen scavenger.  However I think that sounds like way too much for most alloys.

I recall folks using brake lathe turnings *shoveled* onto a particularly weird billet to help to get it to weld in a very very messy trial.

I have come to the opinion that a lot of the functions of flux can be replaced by using Dumbo's Magic Feather and excellent process control.

I have welded without flux so I know it can be done with a reducing atmosphere but some welding operations need a little flux so I wanted to make something that can advantageous to my welding. Brake drums are a ductile iron aren't they?

Used to be Meehanite; I don't know what changes may have been done lately.

Mr. Thomas Powers,

Has mentioned, Dumbo's Magic Feather as a particularly good welding flux.

Sounds interesting and powerful.

Where do I get some?

The SLAG. is willing to give it a try.

Thanks in advance.

SLAG.

"Where do I get some?"---------Check with Timothy

Mr. Powers,

Thank you for the rapid response.

Said response,  though,   is a tad cryptic. 

I am not familiar with a Timothy. Could you please supply me with some more particulars re said Timothy?

Truly yours,

SLAG.

Who gave the magic feather to Dumbo?

Timothy ???

Come to think of it,  I have never met Mr. Dumbo.

Thank you for all your assistance,  though.

SLAG.

I've had some good good success using very fine grained sand as a flux.  It does melt at a higher temperature than borax but is a bit more viscous once it has melted.  My only problem is that the outcrop of sandstone that it was weathering out from when I gathered it years ago now has a Jiffy Lube built on top of it.  I may have to walk the outcrop ridge to see if I can find another location.  I think most beach sand or sand from the big box store for sand boxes would be too coarse.

"By hammer and hand all arts do stand."

If you only had a hammer and an anvil....

We have sand dunes out here and you could select finer sand wind or water sorted.

Mr. George N. M. ,

You have considered sandbox sand from the Big box stores.

The SLAG.  suggests that you may wish to contact a building supply  "store" and check out their silica sand.

Good silica sand comes in various particle sizes, and it  primarily consists of silicon dioxide. Making for a much better bet than sandbox sand.

In other words,  it is less likely to contain extraneous material such as organic matter.  (cigarette buts even).

The cleaner the silica,  the more effective it will function as a good flux.

Just Sayyin' ,

SLAG.

Mr. George,

I forgot to add that silica sand is not expensive. Especially at a building supply store.

Two fifty pound bags of the sand should last a very long time.

SLAG.

Crushed glass has been used and is easily sourced and worked with. (Dirt Daubers nests, rice straw ash, back when working real wrought iron; it's higher temperature tolerance allowed many different silica containing compounds to be used.  One of the nice thing about borax is being able to remove it from the piece with boiling water, rather than chipping it off like glass.)

Simplot has a silica mine down the road from me. Super white sand. Just be careful when dealing with it, as silica inhalation over time can lead to silicosis in the lungs.

If you have a welding supply just buy a can of flux. It's in the torch welding area, with brazing, silver solder, nickle, aluminum, etc. rods. I stopped making my own and now use Peterson #1 blue flux. It's anhydrous borax, boric acid and something to turn it blue. It works as well as any of the "real forge welding" fluxes I've run across. If you really wish to PUT iron oxide in a weld Peterson's Yellow #2 I think is your stuff. 

No need to run borax to 50f. to drive off the hygroscopic moisture, make it Anhydrous. You don't even need to turn it into glass if you warm it gradually before bringing the temp to 212f. Hold it at 190f. for a couple hours then 200 for a while then finish at 230f.

230f. is all the heat necessary to drive off the hygroscopic moisture, more is a waste of electricity though it won't hurt.

Adding about 1/2% carbon in the form of powdered charcoal seems to really help welds to set. Much more prevents the borax from covering the joint surface properly so don't get carried away.

Maybe 1/2% adequately crushed cast iron wouldn't hurt but I doubt it'll do much if any good.

Frosty The Lucky.

Cherry Heat and E-Z Weld both have cast iron filings in them. 

not at 30% they dont, I fear that much is asking for trouble

No actually its 40%

Cherry Heat Compound adheres to ferrous metals at relatively low heat, and is equally good for lap, split, butt, or jump welding. This flux compound enables the blacksmith to weld tool steel, plow open hearth and Bessemer steel at relatively low temperatures making stronger, smoother welds. The flux’s high percentage of metal (about 40%) facilitates the forge welding process considerably. This family of fluxes can be used with both iron and steel.

Highlighting text that way doesn't help anything. 

Frosty The Lucky.