Pewter Lap build

[MakkyBrown]

Just trying 1200 diamond on a pewter 6inch for fine cutting sapphire, producing a very nice pitting free finish and no deeper scratches or orange peel. I think I prefer it to my sintered 800.

MB

[MakkyBrown]

Got this pewter pitcher today, stopped at the local tip shop while passing by. See how it is nice and shiny, and not tarnished. That is due to the high tin content. It is made in Singapore and would be 97% tin. I think this is the best pewter for laps, and perhaps avoid the older pewter that has higher % copper and really old pewter that has lead in it. Paid $8 and it weighs roughly 1.1kg.I think I'm going to put pewter on all my copper laps, in the unlikely event I need a copper lap I can just flip one over and use the back.
Straight tin vs pewter 97%, the pewter is better. Behaves like a pure tin lap but is heaps harder and doesn't round the facet edges as much.
I am thinking of making a triple spit lap 1200/3000/100k for sapphire only. 
MB

[Faceting Frank]

Very nice pitcher MB, would have thought you would have kept it to put your XXXX in and make everyone think your posh.
Pewter is probably what BATT laps are made of, as you can buy ingots of the stuff. I use four BATT laps, one 3k, 14k (which I don’t use much), girdle polish 60k and 60k. I have the 60k girdle polish separate because of the 3k contamination I’ve had in the past imbedded in the rough side of the stone.

[Aussie Sapphire]

Pewter is probably what BATT laps are made of, as you can buy ingots of the stuff.

As per the information provided by Gearloose:

Comparative Hardness of Lap Alloys Hardness (Brinell)
Pure Tin                           5.3
63:37 Tin/Lead solder       14
95/5                                 14
Britannia Pewter        22.5
Sn die cast YC135A        29
BATT™                        32.5
Commercial Rolled Zinc    43

The BA5T alloy is a bit harder again compared to BATT but is quite a bit more expensive.


Cheers Leah

[MakkyBrown]

Thanks Leah, I was trying to post that exact table last night but it glitched

[MakkyBrown]

Very nice pitcher MB, would have thought you would have kept it to put your XXXX in and make everyone think your posh.
Pewter is probably what BATT laps are made of, as you can buy ingots of the stuff. I use four BATT laps, one 3k, 14k (which I don’t use much), girdle polish 60k and 60k. I have the 60k girdle polish separate because of the 3k contamination I’ve had in the past imbedded in the rough side of the stone.

Fortunately the pitcher has a small dent or two so I don't too feel guilty melting it, some pieces I have left on op shop shelves as I figure they'll find a better home than me melting them. The pewter laps might be slightly softer than a BATT lap but far closer to a BATT than a straight tin lap.

[RoughCreations]

For those chemists out there, I scanned my Battlap with a Hand-held XRF unit I had lying around.



It has only 52% Tin (Sn), 12% Potassium (K), 10.5% Calcium (Ca), no Lead (Pb) or Zinc (Zn) of note, very little Antimony (Sb) 0.8%, a little Bismuth (Bi) 1.5%, Sulphur (S) 1.5%.





It also seems to have Thorium 2.7% (Th), lol. Didn't detect any Copper (Cu) of note, either.



The balance (Bal), about 20%, is element(s) the unit can't measure, in this case it is probably Magnesium (Mg) or possibly Aluminium (Al).

Mag-Thor... Google that one, guys.

RC (nervously looking for his geiger counter).

[Bucket]

Far to much time (and technology) on your hands, RC!

[RoughCreations]

Far to much time (and technology) on your hands, RC!

Yeah, you're right, I should be working, any distraction is better!

[MakkyBrown]

Very interesting RC. Looks to be a casting pewter alloy with some other things. Your going to have to do a SG test on it, to see if it is high Mg.  I think I'll stick to my pewter laps without extra additives.2.7%Th is a lot, do XRF machine false positive ?

MB

[MakkyBrown]

Could contain calcium silicide powder, seems readily available.

[RoughCreations]

2.7%Th is a lot, do XRF machine false positive ?

MB

Well, false positives are possible, if it was a rock that I came across in the field I would be sending it off to the lab for a proper determination. The hand-held XRF units are mainly suited to screening of samples, as they only test a very small area each reading. In a rock with many minerals, you have to be aware that many readings must be taken in different spots, it is even more preferable to crush/grind the sample to make it homogeneous. I do remember a few years ago getting repeated high-tungsten readings in some drill core with the XRF, in areas where sphalerite crystals were also present. The high tungsten values were not reproduced in the lab results.
RC