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Platinum dust fusion to gold


#1

Dear Orchid members,

It’s my first post here, although this forum is my go-to resource any time I get in trouble :slight_smile: . Usually I find the answers without asking my own questions, as there is a lot of info available.

This time I was not able to find anything, not saying it’s not there…

So, I am trying to fuse Pt dust to 18k gold with little success and I was hoping maybe someone could point me in a right direction.

I am using 999.5 Pt filings, which I make with a Vallorbe #2 needle file and 18k gold sheet, 0.6mm thick, alloyed with 12.5% silver and 12.5% copper. I paint the spots on the gold with a solution made of gum tragacanth, hard flux and distilled water, roughly 1/3 of each. I sprinkle platinum dust on top of the painted areas and leave to dry.

I get the gold to sweat under the Pt dust with a Little Torch, oxy/propane with #5 tip, slightly reducing flame, by brushing the flame on the surface for a longer period of time.
After the gold sweats I leave it to cool, quench, pickle in warm sodium bisulphate solution and the Pt just won’t stay on. I try to time my heating such that it is the maximum possible without melting the gold base plate, but it’s just a subjective judgement.

I have roughly a dozen failed experiments and one that was successful, but I could not replicate further, although I was using the same setup.

Any ideas on what I could try next would be highly appreciated.

Thank you.

Costin


#2

When you’re heating it, do you move the torch around a bit? I’ve found that sometimes when fusing using similar solutions that there can be some sort of build up that just won’t fully burn off which will prevent fusing unless I move the torch to the side for a few seconds or so.


#3

Yes, I move it around quite a bit. I try to heat the entire base piece evenly and gently brush the flame all around the plate. I preheat the soldering board and heat from above, trying to keep the flame straight down on the piece and move it around.


#4

Sorry, I didn’t describe that quite right. What I meant was that I have to occasionally move the torch completely off the piece once it’s quite hot (on the edge of fusing) to see if any residue burns off. Every so often it seems I have to do that to get things to fuse. Just a thought.


#5

Yes, that too :slight_smile: . I also move the torch off the piece once it’s hot, going back and forth with the tip.
I can do gold dust on gold (18k both) and granulation, both gold and sterling silver (not combined, though…). But I do that with propane only reducing flame on a Sievert torch. It’s the platinum that doesn’t stick, maybe I don’t reach the necessary temperature, without melting it all.


#6

I just tried with bigger filings, obtained using a very aggressive file and some of them fused.

Following a close inspection I noticed that only those that had sufficient contact with the gold base fused, while the others, that were mostly in contact with other filling and only very little with gold, brushed off when using a soft brass brush. So, my conclusion (take it with several grains of salt…) is that platinum won’t fuse to itself (at least not in this scenario) but, in order to achieve platinum filings decoration on gold, I need to make sure that all of the chips have sufficient contact with the base plate in order to achieve the bond with the gold.
I managed to make 5 small Pt granules and fuse them to a gold plate with tragacanth, flux and copper firescale finely ground into a powder (like I use for gold on gold granulation). The result was not very pleasing as I allowed to granules to slightly sink in the gold, but for me it’s progress.

Now, a question for those who do Pt granulation: do you use .999 Pt or .950 Pt for the granules?
Thank you!


#7

Ah, I didn’t realize you were trying to simultaneously fuse platinum to platinum as well as to the gold. Yeah, that won’t work. You’re subject to whichever material has the lowest melting temperature. Otherwise, you can pretty much granulate on anything. . .you just have to know which material will melt first and then act accordingly. For example, when I granulate 18K on sterling, it’s the sterling that will melt first so that becomes the only metal that flows. When I do 18K and 18KW (palladium white), its only the yellow that will flow so you take that into account and watch close as you heat. I’ve even done 18KY granulation on palladium pieces, but the trick to it all is heat/torch control.

So with regard to Pt granulation, either will work, it just depends on what you’re granulating on (though I’ve never tried Pt. to Pt. granulation so I’m not totally sure how that behaves. . still, it will all just come down to torch control). Hope that helps!


#8

Given the melting pt disparities between the two metals, I would guess that fusing isn’t happening at all. This that stick on are likely the result of a process more akin to brazing: a “wetting” of the platinum with the 18k…


#9

Indeed, it’s more like Pt being kept in place by the melted gold…


#10

It does help. Thanks!
So the metal with the lowest melting point will “sweat” first and bond the other one. I just need to make sure that there is enough contact between the small Pt parts and the gold that will keep them bonded.