Most of the stones on the beach will not be polished, but there are many those will be. The harder stones polish best. those that look almost shiny already. Reject those stones which look grainy, they may be hard, but will not polish.
One way of checking the hardness of a stone is to try to scratch it with a sharp knife. If the knife cuts a mark or produces a powdery line, then the stone will not be polished. If the knife leaves a metallic line then the stone is harder than steel and it can be polished. This is not to say that softer stones such as serpentine cannot be polished but that must only be polished with other stones of similar hardness and not mixed with harder stones.
Tumbling times will be shorter with softer stones and a close watch will have to be kept on them, as it will not take so long to grind and polish them. Choose stones those are one inch in diameter or smaller. one or two larger stones may be polished in a load that consists primarily of smaller stones.
Have a look the range of rock polishing machines, grits and spares.
Stone Polishing Instructions:
First Step:
Open the barrel by pushing either end cap off with your thumbs. When new they are sometimes tight, but if you immerse the barrel in hot water they can be easily removed. Squeezing one side of the barrel helps when opening. If you use warm water to fill the barrel it will help to suck on the lid.
Fill barrel ¾ full with stones and shake to settle. Do not use less. it will not work as there is no tumbling action unless the barrel is filled sufficiently.
Add water to just over the top of the stones.
Add one heaped tablespoon of coarse silicon carbide 80 grit for a 1 ½ lb barrel or 2 heaped tablespoons for a 3lb barrel and 3 heaped tablespoons for a 5 lb barrel.
Run the machine for a few days and nights while occasionally examining the stones. Fairly smooth pebbles might need only about 3 days to become nicely rounded while very jagged ones may need 10 or more days running and the grit topping up to get the same result. Seven days is a reasonable average.
Second Step
clean the stones completely and barrel by removing both ends.
Proceed as before using 220 grit this time .It should only be necessary to run this grade for about 5-6 days .
Third Step
Clean stones completely and barrel by removing both end caps, washing carefully.
Proceed as before using the same proportions of grit and water but this time use 400 grit. Please note this stage is very significant and determines the final polish, it is vital you do not make it short.
Allow at least seven days tumbling. Please do not top up with fresh grit as this will re roughen the stones .Each day on this stage imparts a smoother finish as the grit breaks down and progressively smooths the stones making it far simpler for the next step
Fourth Step
Clean the stones very carefully and barrel. It would be useful to keep one barrel to be used specifically for polishing only, because of the difficulty of cleaning grits completely from the sides of the barrel. Additional barrels can be purchased separately. Examine the stones very carefully and make sure that those are very smooth. Discard any stones that are badly cracked or have jagged edges- they can be re tumbled with your next load.
Repeat steps as before using similar amounts of water but one level tablespoon of cerium oxide instead of grit for a 1 ½ lb barrel (adjust amounts accordingly for the size of barrel as with the grits). If the barrel has been cleaned out properly and the previous steps are carried out correctly 7 days running should produce gleaming stones. Remember as with all things practice makes perfect.
Do not put any of the resulting slurry down the sink. it is inclined to set solid.
i hope you will find all this above information very useful. if you need any further information please contact me by mail or phone.
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