How can I disguise flaws in bronze with a patina?

Discussion in 'Castings, finishing/ repair/ and patina's' started by DJN Holistic, Jul 30, 2022.

  1. DJN Holistic

    DJN Holistic Copper

    I'm working on a piece at the moment, but I'm struggling to find a patina I like. My cast is okay, but has plenty of minor imperfections. These are barely noticeable on a untreated bronze without close scrutiny, but stand out a lot when applying a patina by creating contrast and reducing the visual quality of the piece.

    The kinds of defects I'm talking about are:

    Pinhole porosity marks
    Uneven texture in the grain.
    Nicks and scratches that existed in the wax model.
    Colour difference between brazed sections and the bronze.

    Has anyone found a method to work around this?
  2. HT1

    HT1 Silver

    wow, you are all but asking for a miracle , 1 and 3 can be brazed and sanded , 2 can be disguised with sanding/polishing , 4 is a killer, you are going to have to work with something closer to a heat set stain rather then a patina, patina s are created by a chemical interaction with the metal, so different metals will patina differently , no getting around that ,

    I had a long talk with a gentleman from an art foundry that was doing some incredible patina work on Instagram,

    his advice, be absolute perfect on your alloy, and match your braze or tig filler perfectly to that alloy, even if you get a color match, but not a chemical match, patina whether natural, or artificially induced , will not color match on two different chemically alloys, and braze (in the way welders use the term) will not chemically match, not even close... you maybe referring to torch welding , which looks like brazing but is different .

    patina, and then use a tinted heat applied sealer to blend the colors . I know this really messes with the purist in metal workers mind, its cheating, but it maybe the only way to make what you want happen, I have no more detail then that Sorry

    I wish I could point to his work, but he was applying "patina" with a brush and hitting it immediately with a torch, this allowed him to much like an oil painter to add layers each getting darker.
    this is a really specialized skill, way over my sand packing education

    V/r HT1
    DJN Holistic likes this.
  3. Mantrid

    Mantrid Silver

    A picture of the piece will help us provide a suitable answer
  4. DJN Holistic

    DJN Holistic Copper

    Couple of pics of my current piece.

    Side view shows the kind of pin hole pours I'd concerned about.
    Second shows the braze work where I filled a shrinkage hole.

    I've seen recipes that list sodium silicate as part of the process of applying patina. I guess it acts as a filler and sealant. It sounds like it's the answer I'm looking for, but I can't find any information on the specifics. I'm a little hesitant to start experimenting with it without a nudge in the right direction.

    Attached Files:

  5. Mantrid

    Mantrid Silver

    Little pin holes like that can usually be ground out. You may have to take some material off the whole side so it doesnt leave indentations in the piece. I take it you do not wax your finished bronzes, as those little holes usually disapear sufficiently when they fill with wax. If the porosity is extensive then your either recast it or invest in a welder.

    Same thing with the brazing. If you are doing this often then you need to work out why you are getting shrinkage, or again get yourself a welder. I tend to cast rods along side mybronze that I use as a filler rod for welding openings shut. As the rods are the same alloy as the piece they always match. Only other solution is to use a black patina that will mask the metal sufficiently.
    HT1 likes this.
  6. DJN Holistic

    DJN Holistic Copper

    That's a really good idea! Going to have to try that. I have a ton of 5mm cut off sprue that should do. I'm not sure if my torch will be hot enough though. It's just a small oxy/propane torch.

    Not really an option for this one as I'm aiming for a light tan/sandy colour. Honestly the creamy base colour of the bronze is close to what I need. It just needs a bit of shading to give it some depth. Haven't decided how to do that yet. Maybe a weak sulphur dip and sand it back down.
  7. Mantrid

    Mantrid Silver

    I dont have experience of welding with oxy/propane, I havent heard of it so I suspect it cant be done, not with bronze anyway. The only method of welding bronze I know of are with traditional welding machines such as tig mig and stick. I use tig as its more precise with the small bronzes I make and it requires a shielding gas, usually pure argon.
  8. Petee716

    Petee716 Gold Banner Member

    Maybe I just got lucky, but I did this repair using oxy/acetylene and some stringy scrap as filler which was generated during the pour. I used borax as flux.
    I didn’t try to tackle the smaller surface defects, just the major one on the border, but the patina helped to obscure the surface porosity a bit. Again this was simply torch heated with a rich oxy/acet flame till it went black and then quenched and spray lacquered after sanding the high surfaces.
    229794D5-BFD2-43B9-A93B-1917A7411511.jpeg 529C6855-CF4A-4081-B56C-2A32155ED2D7.jpeg 2BB76B93-F118-4710-933B-C4E1F2718424.jpeg
    Alloy: everdur
  9. mytwhyt

    mytwhyt Silver

    I've saved gold and silver castings that had surface porosity by burnishing the surface. I use my Foredom flex shaft and a bur with the cutting end removed. After heating the end till red you can bend 1/4" at a 90* angle,, Works best if you sand and polish the end. You'll be surprised at how it will compress and move the metal to fill the porosity. It'll only need slight sanding to smooth again.. I usually use a split mandrel and a strip of sandpaper. Most of the work I do has been finished at a jeweler's bench..
    Last edited: Jul 31, 2022
  10. DJN Holistic

    DJN Holistic Copper

    What is a flex shaft? It looks like a fancy multitool. What are the advantages over a Dremel or some such?
  11. mytwhyt

    mytwhyt Silver

    A Dremel will serve the same purpose. A simple way to hammer and compress the metal.. The difference between a Dremel and a Foredom flex shaft is a couple hundred dollars. I bought my first one in 1970 when I decided I wanted to be a jeweler and make jewelry.. I've realized several times since then that I would have been better off staying as a Mailman.. I have a hammer handpiece that hammers up and down.. The simple bent tool seems to work better with the slightly larger porosity.. I use the hammer handpiece for setting bezel set round and oval stones.. That said, you need to be very careful not to girdle the stone.. Nothing pisses a customer off like chipping their stone....
  12. You could try a hand matting tool - either buy a set, I got mine from a model engineering place, or get a counter punch and flatten the end (sand it to remove any sharp edges that might dig in)
    tap very lightly with a hammer and 'push' the metal closed, may work, may not - practice on a scrap piece first in case you don't like the marks. then you can sand back. also if the holes are too big you could try a tiny piece of bronze scrap and push from the middle outwards to matt into the main surface, from your pics I don't think any are too big for the normal matting method.

    Patina wise, echoing what others have said but I wonder if you went with strong ferric you could get away with layering it at different strengths in different areas - it would be fiddly so again practice on scrap. Might not be the colour you want though.

    Tig welding is a breeze in comparison, I recommend the investment in this.
  13. Tobho Mott

    Tobho Mott Gold Banner Member

    Is "matting" what you call the old school way this guy fills in little holes in bronze sculptures?

  14. That is correct sir, takes finesse (which I rarely have) but can produce good results - have to be really careful not to create too many new marks that you then have to get rid of, hence practice. the metal burrs used around 18.25 can also be used to 'push' but will leave extra marks that you may have a fun time chasing back.
    Tobho Mott likes this.
  15. DJN Holistic

    DJN Holistic Copper

    I managed to smooth out most of the flaws using a combination of grinding disk, burr, rasp and sanding drum. Only about four pinholes remained which were being too stubborn to remove. Trying to remove them was gradually creating indents, so I cut my losses for those last few.

    What proved a greater challenge was finding a patina that didn't enhance the flaws. While invisible to the eye and touch, with all the cutting, grinding and sanding on large flat areas, the surface was hiding a texture a bit like a peeled potato. Once a patina was applied, the subtle edges and indents revealed themselves.

    I tried several methods to get an evenly applied patina. Dipping, boiling, fuming. None of it looked very good. In the end I decided to "paint" it with a torch and an air brush loaded with ferric nitrate solution. It was difficult, because it's like painting with invisible ink since the colour didn't appear with the brush stroke, but afterwards once touched by the torch. This meant that I had to go by instinct when applying colour, and there was no way to correct mistakes. For a first attempt however, I think the results were quite good and I think I'll use this method again in the future. It's definitely a technique that needs practice to master.

    Attached Files:

    Tobho Mott likes this.
  16. Holy moly that's a handy tool, is it something you can buy or was it home made? Going googling....

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