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Offline HobbyistTopic starter
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« on: March 28, 2013, 02:03:23 am »
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Hope someone knowledgeable on chemistry can answer my question. Please find attached a photo of my streak plate with a metallic gold streak on it. There are 3 drops of fluid on the streak. From top to bottom, they are:

Fluid drop #1) 9k gold test acid diluted with a similar sized drop of water and thoroughly mixed together.
Fluid drop #2) Plain tap water
Fluid drop #3)  9k gold test acid, straight from the bottle.

I hope the photo is clear enough after resizing. Drop #1 shows some undissolved particles after approx 3 minutes. Drop #2 has zero reaction, as expected. Drop #3 dissolves 100% of all particles.

My question is: when 9K test acid is diluted with an approximately equal amount of water, is the mixed fluid an accurate test of 4.5k gold? Thanks!

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"Gold rides an iron horse." (Old prospector Homefire)
Offline GoldDigger1950
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« Reply #1 on: March 28, 2013, 04:45:51 am »
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The dilution only makes the test take longer. There is a specific mix of acids which cause the reaction to the test.

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It's all about that moment when metal that hasn't seen the light of day for generations frees itself from the soil and presents itself to me.
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« Reply #2 on: March 28, 2013, 05:31:06 am »
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OK Thanks GD. Was hoping to avoid the cost and waiting period for more fire assays, looks like its unavoidable now.

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Offline GoldDigger1950
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« Reply #3 on: March 28, 2013, 06:09:55 am »
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One method you can use is to take a known sample and mass. Let's say 22k, 4.78gms. Trim it to 4.0gms. Take a known mass of your new sample and try to get as close as you can to 1.0gm. Melt them into a homogenous ingot and test for your purity. Your result might be something like 15.7k for the 5gm total. Knowing that 20% of your total is an unknown purity, you can calculate what your sample would be. Your sample reduced 80% of the original sample by 6.3k so this can be extrapolated by simple averaging to determine the missing sample purity.

I'll leave the math up to those who like a bit of a puzzle. Good exercise for the brain. You could also make the known sample a 1gm sample which is far easier on the math but less accurate on the resultant purity estimate.

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« Reply #4 on: March 28, 2013, 06:31:59 am »
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I understand the math, and that method makes sense. I won't be able to perform the purity tests of the homogenous button down to decimal figure accuracy, but my testing acids should allow me to extrapolate a ballpark karatage of the unknown sample, and that's good enough for me (I don't intend to sell any color). Will get some scrap 22k gold from my goldsmith after Easter weekend and give it a go. thanks again!

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« Reply #5 on: March 28, 2013, 06:38:11 am »
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Great. I figured you might only need a rough estimate. I used 22k because a lot of raw gold is close to that but you can always use any purity and still extrapolate. All you need is a known mass and purity for your control and a known mass for your unknown sample. A spreadsheet will also be handy if you have to do it more than once.

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« Reply #6 on: March 28, 2013, 03:08:31 pm »
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I'm hopping that this thread will continue

All the best to all
Xavier

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So many questions so little time
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« Reply #7 on: March 28, 2013, 04:00:30 pm »
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Quote:Posted by xavier
hopping that this thread will continue

Same here Smiley

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« Reply #8 on: March 28, 2013, 04:27:54 pm »
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The Lowest K Marked Gold I've ever seen was 8K.

I never bothered to test it as was.

I just Flattened it out on a Anval and Rotted it in Nitric.   

What Was Left was Gold.  LOL Not Much.

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« Reply #9 on: March 28, 2013, 11:44:57 pm »
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Quote:Posted by xavier
I'm hopping that this thread will continue


Yes this thread will continue, rest assured! Smiley

Quote:Posted by homefire
I just Flattened it out on a Anval and Rotted it in Nitric.


That would have been the most expedient method, homie. I had obtained a quote from a lab supply company for a 2.5 liter bottle of 65% HNO3 (it's cheap). The manager warned me that I would have to register with valid ID in order to buy, and that her customers were currently subject to visits and questioning by the police, as well as inspections by the health dept. If you  google "acid attack Malaysia", you'll get numerous results of people getting splashed with acid, and there are quite a few copycat sickos doing it. While I have absolutely no intent of such acts, the thought of being pestered by various authorities put me off buying a bottle.

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