in regards to the primary regulators: they reduce the tank pressure that feeds into the secondary regulators. a full oxygen bottle (mine is 150 or 200 cubic feet at 2,200 psi) has too much pressure for a direct feed into the hose, even if throttled down. opening up the primaries will allow a higher pressure at the secondary regulators and allow for a higher gas pressure in the hose and a higher flow of gas. But you still don’t want to over pressurize the secondary regulators, as doing so could damage them… A single stage regulator is not safe nor controllable with pressures as high as a full bottle of gas has…
Propane tends to be much more clean burning than acetylene. That’s because there’s an excess amount of carbon compared to hydrogen with acetylene… that excess carbon is what makes acetylene burn so hot…I’ve used acetylene mostly for steel sheet cutting and heating… there it’s necessary as steel working requires a lot higher temperature. Not so with precious metals, and small pieces. most of my work with fabricating has been done only with a hardware store propane air torch…
I’ve also used oxy propane which is much hotter. If you are working indoors, even oxy-propane and propane air torches generate high enough temperatures to create nitrogen oxides… the build up of NOx, within a poorly ventilated closed space will become irritating… the same problem with automobile exhaust even after passed through a catalytic converter…a reducing flame will create more pollutants, as combustion is incomplete. A hot oxidizing flame will create more NOx… so not matter what you use, you still will be creating some indoor air pollution, unless you have an exhaust fan over your work area… for small scale work with nontoxic chemicals, an exhaust fan would suffice… if you are using volatile acids, such as nitric acid and hydrochloric acid, cyanide solution, or fluorides, then you will either have to do it outdoors and stay upwind of the fumes or use a vent hood…all of the fumes from these chemicals are corrosive or highly toxic. I go outside to do melting and pouring…and that is only when the weather permits…
So far as learning new things, all of the world’s knowledge is at the tip of your fingers… you can google anything on the internet… understanding some rudimentary chemistry about the processes you are working with is a good starting point… for me, the learning curve has been trial and error with advice from books and technical specs from the internet… not matter what you read and how closely you follow instructions, you can’t expect something to come out perfectly on the first attempt… you’d get something satisfactory but not perfect… it’s still a matter of learning from doing… the books and internet tell you what’s possible and what’s not… books tell you how to do things within what’s possible, but don’t guarantee a perfect result the first time around… experience builds up slowly. The main thing is to have fun at doing what you’re doing… I love metal work because hot metal is alive…Heat transforms something that is inert and obdurate into something that is pliable and can be shaped to your will, within limits of the material that you are using…it’s a great feeling to do that… so ENJOY!!! experiment and don’t fight it…have fun with it !!!
you are correct sir!
You’re so knowledgeable about all of this that my head is kind of swimming. I like it! I did play around with it the other day, the settings on the tank, the pressure. I had some molten sterling, if I turned the oxygen up high so it was roaring, the metal started to solidify, if I turned it down it liquefied, just trying to find the right balance. So I gauged it in that way, playing with the settings (at a reasonable and safe pressure of course), and I think I found the sweet spot, I had a successful cast. I have really crappy lungs, asthma, and horrible deadly allergies to certain chemicals and my airway likes to randomly swell shut just cuz. I value my ability to breathe, so I’m always ultra careful with chemicals. I have fume extractors, fans (not blowing towards whatever I’m heating but angled to suck in fresh air and hit me in the face with it). Air quality and ventilation are important to me, and I haven’t had any issues at all so far. I think I’m going to get some more fume extractors, though, because I’m really paranoid about it. I REALLY hate it when my throat swells shut, that generally sends me over the edge into full blown panic mode. But I followed your advice, just testing the balance and trying to find the right balance, learning what the flame looks and sounds like when it is correctly balanced. I’ve casted several ingots so far, seems good. I’m finding, though, that a lot of borax is often fused to the surface of the ingots I cast. I mean I file it off, sand it down, and with the wire I’ve drawn it just sort of disappears. I’ve never seen any ingots come out looking like mine whenever I’ve watched the videos on how to do this, they usually look pretty clean. Why would the borax be fusing into the metal? I thought maybe, even though it’s practically brand new, the crucible needed to be cleaned, so I cleaned it out, melted all of the old borax out from the previous cast, added new. Nope, my ingots are still coming out marbled with borax all across the surface. Seems mostly fine underneath the surface, though. Not sure what the problem is?
So I’ve got a question. I’ve heard some goldsmiths say they use arc welders? These are goldsmiths who only work with precious metals, not anything ferrous. Why would a goldsmith need an arc welder? Under what circumstances would an arc welder be needed by a goldsmith?
At some point I definitely want to find someone I could hire to come to my workshop and show me some things, answer some questions, and clarify a few things. I’m not able to really leave my home at the moment, and I may never be able to, going out for long periods of time isn’t really an option for me so I’m all home-based. Are there goldsmith teachers who make house calls? That would be awesome.
So does all of this stand true for the refillable tanks? I’m not using the disposable ones, I just take mine to the Airgas store and get them refilled when I want. But if you can’t use the rosebud tip with a tank less than halfway full, I need to keep an eye on it to take it in more frequently and get it refilled!
Hi Dana,
I am only familiar with the small disposable propane tanks.
julie
I’ve used oxygen/gas mainly to do steel work, making mobiles and windchimes out of scrap metal.
Acetylene oxygen is required for that, by using a cutting torch tip. It takes a lot more experimenting and adjusting the gas flow to do steel…I’ve learned by trial and error how to optimize the flame for its intended purpose. I’ve used the cutting tip for melting silver, and also the same torch for propane, using a bottle from a gas grill… bulk propane is a lot cheaper, but you do need to have an adapter to get it to fit together…If you were to use a gas grill bottle, the single stage regulator that comes with the grill that is built in is what has to be connected into the gas end…only the oxygen end connected to your high pressure 02 bottle goes thru the two stage regulator.
For melting, I’ve used both propane and acetylene… I still prefer acetylene because it burns so hot that it get the job done quickly…but i have to do it outside… I can’t have spilt molten silver during a pour, fall on the floor and burn a hole thru it…nor stink up the house with fumes.
I see that you have a couple for problems… you do need a large flame to do melting but if you are turning the oxygen up too much you will get an oxidizing flame…although oxidizing flames are very hot, the relative lack of fuel gas is causing the temperature to drop, the only hottest part of an oxidizing flame is at the very inner cone, which will shrink in size as you turn the 02 up, while turning dark blue…you are ending up blowing oxygen on the silver and not enough fuel gas.and dropping the temperature. by turning up more propane, you can restore a neutral flame, but you can’t keep on turning up both gas and 02 before you overload the capacity of the torch and blow out the flame…if the flame is roaring there’s too much gas/oxygen passing thru. …balancing the flow of gas and 02 takes playing around with,… you’ll get the hang of it quickly…the silver is remelting at a balanced flame and you have already found the sweet spot…
The borax problem is what I have run into also…too much borax in a melting dish in preparation to do a pour causes a buildup that is a sticky mess in the bottom of the dish… I’ve melted raw ingots for use later, and right now I have one that is stuck in… I would have to remelt it all and pour the silver out into an ingot mold to get it out in a useful form…the dish itself is still overcoated with sticky borax… some of it can be dripped out by really heating it hard, but most of it remains stuck…solid borax glass residue is intractable to soaking in water to dissolve it… I really don’t know what to do except to grind it off…I did not have this problem with the old fluoride fluxes, but fluoride was discontinued year ago, because it’s just too dang toxic!!!..I haven’t had a problem with borax sticking to poured ingot in a mold…you’re not supposed to flux a mold at all…the mold has to be very lightly oiled, using vegetable oil or vaseline and heated until it’s smoking hot… the oil actually carbonizes to a thin layer of carbon very fine dust that keeps the silver from sticking to the steel sides of the mold… the silver that’s poured in should not have any excess flux floating on top…that would gum things up… for melting, you almost don’t even need to use flux…very little at all…
I am able to get my silver for free… I’m a medical subspecialist that reads brain wave tests… gold plated silver electrodes of about a half cm diameter are placed on the scalp to record brain waves… after awhile, the wires break and the electrodes and attached wires are thrown away… I’ve asked my techs to give me all of the throwaways…I haven’t tested the fineness of the silver commercially, but I’m pretty sure it’s fine silver…I did attempt to extract the gold plate chemically as an experiment but that was a disaster… Using hydrochloric acid with a little bit of nitric acid dissolved all of the silver, leaving the gold plating behind… the plate was like gold leaf… it was so thin, just a couple of microns, that even trying to fish it up with a wooden disposable chopstick caused in to tear…filtering the silver chloride solution thru a coffee filter caught the gold, but the amount present was so small that it wasn’t worth the time and the chemicals to do so… I’d have to process a thousand lbs of silver to recover one ounce of gold… recovering the silver out of solution was also a disaster… the silver was precipitated out of solution by the addition of table salt, turning it into insoluble silver chloride… silver chloride will spontaneous breakdown into silver metal by heating… except the precipitate was so fine that it ran right thru a coffee filter…it would have taken a biological science grade millipore filter to have trapped the precipitate, at an astronomical cost…So whatever silver ingots that I can make of the electrodes have a trace of gold in them…I’m sure they are fine silver. By using my cutting torch, I can inject a stream of oxygen into the molten metal. the oxygen burns out all other metals, except for gold…fine silver will also absorb 60X it’s volume in oxygen… as it cools, it forms bubbles of oxygen that exsolves out of the silver… the bubbles bursting make it “spit” bubbles of 02…dangerous and must be done outside… this is the basis for fire refining of silver… to make sterling again, you’d have to remelt it along with 7.5 weight percent of copper., using a neutral to slightly reducing flame so as not to burn out the copper.
But I’m digressing… back to your problem of borax sticking to ingots… when melting scrap, pickle it completely first to make sure it’s completely clean…wash it well…you really don’t need to use much if any flux at all when melting it…the dirty metal will float on top, and you can try to pour it off without pouring in the less pure metal… if you do pour it in, and the ingot mold is hot, it will rise to the top of the ingot…where you can file it off…
Your last question about arc welders will apply to laser welders also. They have the tremendous advantage by applying a very high temperature… over 7,000 to 10,000 degrees to a very small area…0.5 to 1 mm in diameter…as long as the metal is clean, there’s no use for flux. The heat is so intense, but yet so concentrated that it will spot weld two pieces of metal together…the area of weld will be thin, but by varying the energy of the pulse, more penetration can be achieved for a stronger weld. This has a tremendous advantage in fabrication, since things can be tacked down for further soldering, if joining large pieces, or used alone in welding down the base of a small prong without heating the whole piece up…no added metal is necessary, although a very small piece of gold or silver can be added for a bigger weld covering a larger area…I haven’t invested in buying either, since I’ve done all my fabrication using only propane air torches from the hardware store…it’s much harder to control because the whole piece gets heated up…but again it’s just a matter of experience and trial and error… not matter how carefully you plan something, the first try is never 100% satisfactory…my experience with arc welding has been to join steel… I have a MIG welder that is a relatively low powered one that produces not a pulsed arc but a continuous one for welding steel…the temperature it generates is about 10,000 degrees…yet it’s running at 120 amps, 24 volt output ( 2,880 watts)… any high current arc even if in a millisecond pulse generates a very high temperature… eye protection is need not only to see what you’re doing, as the arc is brighter than looking at the sun, but also creates ultraviolet light which is harmful to the eyes…a continuous high power arc also requires skin protection from sunburn… but that’s not the case with pulsed jewelry arc welders. A shielding glass however is necessary to see what you’re doing and for eye protection…
There have been many other contributors who have used both laser and arc welders… they are on a different thread, but if you are interested, you can ask those people how they do things and deal with problems… But since you already have an oxy propane torch, you need to get used to it for multiple purposes, from annealing, soldering, and melting…I think that will be more than satisfactory for a hobbyist. arc and laser welder are expensive, if you get a good one, but they are now indispensable for jewelry repair and professional applications… It took me 5 years of experience and continuous experimentation to get decent at fabrication…I haven’t sold anything, as it’s a hobby…and I want to keep them… but the evolution of my work does show a progression from simple towards more sophisticated…
Good luck, best wishes, and have a lot of fun doing it… forget the frustration, it’s all part of the learning curve…I’ve learned more from my mistakes than what books could ever teach me.
One last comment: over the last 30 or so years, there’s been a micro sizing of industrial technology making it applicable to doing small work, like jewelry, on non ferrous metals. from downsizing torches, to the adaption of inert gas shield welding, including TIG which uses a high frequency alternating current arc developed for welding aluminum. to laser cutting and laser welding, technical innovation has revolutionized the old traditional ways of doing things, much to the better…I have a book written in the late 1800’s that used a mouth blow pipe into a candle or water gas (carbon monoxide hydrogen) flame… ancient craftsmen in Egypt and the Americas were able to create stunning pieces of jewelry by just using charcoal…
No Dana - the full size tanks can be used to nearly the end. It’s the little ones that have less pressure and as they empty the pressure is too little. fill the tank when it quits working.
Judy h
Assuming you have an account with Rio Grande, Stuller, Hoover & Strong or United Precious Metals, you may be better off sending the ring for refining for store credit and buy fresh casting grain or other milled products.
Based on your comments, I’d say you had voids in the casting that were not subsurface, but close enough that the heat applied caused the surface metal to move, opening up the pits – OR – your alloy isn’t quite sterling silver. Sending it to refining is a sure-fire way of figuring out the metal fitness.
You make excellent points! I’m planning on taking some metal to the refinery soon, I’ll throw the silver from that ring into the tray. Better safe than sorry.