reaction time

[Geo]

i normally deal with electronic scrap but wanted to try some jewelry just for the experience so i bought about 50 grams of sterling silver rings and chains and about 30 grams of mixed gold chains. on one chain there was a medallion that was stamped 1/10 14 kfg which weighed 8 grams. i put it in a beaker and poured in 50 ml of hcl acid and started adding nitric acid slowly, a few mil's at a time until i had added 25 ml. i waited for a reaction but it never occurred so i applied a little heat, just enough to get a steam in the cool night air and still no reaction. i checked all of the pieces before i bought them and am sure its all genuine. how long before i should expect a reaction to occur?

 

[Geo]

ok. never mind about the time.i checked on it 90 minutes after mixing and the medalion is gone and the solution is a dark green and very thick. i removed the glass off the top and there was no red fumes and there is some white looking bits of metal left in the bottom. still cooling so i cant get a weight on the metal remaining but from the looks of it may be 1 gram to 1 and 1/2 gram remaining. does this mean the acid was depleted or is there a metal that doesnt react with AR?

 

[Harold_V]

You've been on this forum long enough to know my attitude about processing gold along with base metals. Why you'd process a gold filled object that way escapes me, but maybe there's something you'd like to share with us so we can understand why you made that choice.

Harold

 

[Geo]

that was my first time trying to process that type of material. there was no definition between the gold or base metal like in a gold filled watch band there wasnt even a layer that i could see. it looked like one piece of metal with nothing to pry off or take apart. i had studied on it all day trying to figure it out for myself before i tried and the only thing i could come up with was to dissolve the whole thing like it was.

 

[Harold_V]

The layer of gold can appear to be a constant, depending on the nature of the base metal, and the method of attaching the gold layer. It is VERY common for the base metal to be of brass, so when the gold layer is worn, the base metal still resembles the gold surface.

Next time you wish to experiment with gold filled, you have two options. One of them is to use it as added metal when inquarting. The numbers tell you how much gold was present when the item was made, so you can calculate how much gold and base metal are being added. It won't be deadly accurate because wear on gold filled objects tends to be only on the gold. Yield will generally be somewhat lower than that which was calculated, as a result.

The second option is to digest in heated dilute nitric. No need to do anything aside from incinerate before the process, and to remove any ferrous or aluminum pieces should they be there. In spite of the gold layer, nitric will penetrate readily and digest the core, leaving behind either small particles of karat gold, or even a sheet. All depends on the nature of the piece, and the condition of the gold.

It's always wise to eliminate base metals before dissolving values, with rare exception. That's particularly true with gold filled, which has the potential to have lead and tin included.

Harold

 

[Geo]

i didnt even consider trying nitric first. i now have that in my notebook. thank you for the information. i did consider cutting it in half though making two disc to see if it looked different on the inside. i have passed on gold filled in the past because i didnt know what to do with it. i still have a heavy wrist watch here that is gold filled 1/20 18k ive had for two years thinking id find a way to extract the gold from it. ive seen the other post about watch bands, i think ill have a go at it next. remove gold covered plates and incinerate then immerse in warm dilute nitric acid till the base metal is dissolved then process the gold. got it, thanks again Harold.

 

[Harold_V]

i did consider cutting it in half though making two disc to see if it looked different on the inside.

That's generally a useless test. You will rarely be able to identify internal materials by snipping. The gold filled surface streaks across the base metal, so they are difficult to identify. Such tests are generally best accomplished with a file, cutting a deep notch in an edge of the part. A drop of nitric applied to the notch will disclose the nature of the part.

Harold