Quote from: Oldandcreaky on July 28, 2024, 08:09:51 PMCan you share one before photo of any stone? I'm curious how you descry the potential in a rock? Is it purely your expert eye and is a stone with potential something an untrained eye like mine might spot?
The first thing to look for is: "Do you like it?" Is there something that appeals to you, such as shape, color, clarity, patterns like banding, and so forth? If you like the shape, tumbling it will knock off any rough edges and smooth them out. So things like crystals are not good candidates as it would ruin the shapes of the crystals.
Next is the type of stone and this is tied to the stone's hardness. The Mohs Scale ranks stones from Talc (1) to Diamond (10). If you know the type of stone, you can determine its hardness. If you don't know, you can test it. If you can scratch it with a fingernail, it is soft, less than 2.5 hardness. If you can't scratch it with a fingernail but it scratches with a copper penny, it is less than 3.5, and so on. I use a steel nail or a file (6.5 hardness). If it scratches, it will need a closer look and may be too soft. If it doesn't scratch it is in the 7.0 range which puts it in with quartz, jaspers, and agates. The harder a stone is, the better it will take a nice shine.
Testing the hardness is the best way to go unless you know exactly what the stone is. Some stones can be bought on the internet or in reputable rock shops but they use "trade names" to make them more marketable. But the names are very misleading.
This stone is marketed as "Pimento Jasper" or "Fruit Jasper". I had many issues with it, so I did some research. It is not Jasper at all. It is called Sabalgarh Marble and it is from India. Marble is a soft stone, which is why it is used in sculpture (it is easy to carve).
Because it is porous, the polishing grit darkened the color. Because it is soft, much of the stone's mass wears away very quickly. The porosity also prevents it from taking a shine. I had to spray it with clear acrylic to seal it and make it a little more durable.
This is called Fuchsite, also called Chromium Mica. It is very soft (4 -5 hardness).
The mica gives a nice silver shine, but the stone is quite porous and flakes off under pressure. I had to polish this by hand so I could control the outcome. I have since learned that soft rocks are often not used in jewelry because they are not durable enough. Jewelry gets dropped and knocked around and soft stones can't take any abuse.
This is a piece of agate. Agates rank at 7.0 hardness. The only things harder are Topaz( 8 ), Rubies and Sapphires(9), which are the same stone just different minerals change the color, and Diamonds(10).
Notice that the grit did not change the shape much. Agates are a 7 hardness and the grit we use is about a 9.25 hardness. I did not leave it for a full cycle so that I could preserve the shape. Then I moved it into the smoothing and polishing phases for the final finish.
I belong to a few rockhounding and rock-tumbling forums and we often get questions from members to identify rocks that they have found. People far more experienced than I can usually tell if it is a good candidate for tumbling. If I have doubts, I throw it in the tumbler for a week and see what happens to it. Sometimes disaster, sometimes treasure.
I also have rocks that I consider too precious to risk in a tumbler, so I either hand-polish them or leave them as they are. I have a candy dish that my late uncle made when he worked in a bronze foundry. That candy dish is filling up with stones that won't go in the tumbler.
One last thing is size. The tumbler reduces the mass by as much as 25%. So if you start with pebbles, you will end up with sand. But you also can't go too large either. It must fit in the barrel of the tumbler with enough room for medium and small stones to roll around with it. My barrels have a 3-lb capacity. I have 3 machines running a total of five barrels at once. So I am tumbling 15 lbs of rock 24/7. It is the stones rubbing and sliding against each other that give the grit its abrasive power. Fill it too full and the rocks can't roll and slide. Not filling it enough will cause the rocks to get thrown around (think clothes in a dryer) and the rocks will get chipped and broken. I like golf ball-size stones, as they end up just the right size. Any bigger and I "resize" them with a 3-lb sledgehammer. If that would ruin it, it doesn't get tumbled.
I know a few people who choose only rounded stones, like you find in rivers or on lake shores. Mother Nature has already shaped them and sized them so they can skip the first stage and move right to smoothing and polishing. Some people have found some amazing rocks in their driveway or landscaping stones. Another guy uses Google Earth to locate houses with rock-covered roofs. He gets permission from the owner and climbs up. He has found some great stones there too.
The nice thing about rockhounding is there is never a shortage of rocks.
