The first phase of the tumble is known as the "Shaping Phase", it is during this part of the cycle that you will be grinding the stones
virtually down to their final shape and size. For this phase you will use 80 Grit, the most coarse grit in the selection. Subsequent grits will not shape the stone, but merely scratch the surface slightly -
over and over again until it becomes smooth enough to polish.
Take the barrel labelled "80 Grit" and place 2-3 table spoons of plastic pellets into the barrel.
Now place enough stone in the barrel so that it reaches
3/4 of the way to the top. Do not underfill the barrel, as the pieces will not tumble, they will slide up and down the side as it turns and flats will form. Do not overfill the barrel, as there will not be enough
room for the stones to manouver much and they will not grind efficiently. Tap the barrel on the side to flatten out the surface of the stone as much as possible.
(REPEAT FROM HERE ONWARDS IF NEEDED)
Place 1 and 1/2 heaped tablespoons of 80 Grit into the barrel per 1 and 1/2 LB of rock used. So for a 3LB barrel place 3 heaped tablespoons in. This is a rough guideline - the harder the rock the faster
the process is with more grit (only around 1 tablespoon more though) the softer the rock, the less you can use - (again - only around 1 tablespoon less). With 1 and 1/2 of 80 Grit per 1 and 1/2 LB of rock
you can't really go wrong.
Once the grit is in, fill the barrel with COLD water until it is just about covering all of the stones. There may be one or two "peaks" sticking out, but this is ok as long as 90% of
the stone is completely submerged. The reason for cold water is that for the press on type of lid, hot water expands the plastic, and you don't want your lid warming up and coming off when its on the machine!!
Place the lid in boiling water for 2 minutes, if
is the kind of barrel you are using, until it softens, then press it onto the barrel, lifting the edges to expel excess air. Once in place allow it to cool and contract for around 5 minutes - or simply fasten the lid on tightly for other types as per the instructions provided with the machine.
Once the barrel has been prepared with its contents, place it on your running tumbling machine.
Now comes the hard part - leave the barrel alone for 5 days. Let it roll for 24 hours/day for that period, time
is of the essence here, remember that nature takes thousands of years to act on stones in the way your barrel will in just 5 days!!
The reason I leave this for 5 days, is because the silicon carbide 80 grit often
breaks down fairly quickly, so with each passing hour there is less and less effective grinding grit left in the barrel. I find that with a good range of different sized pieces of rock, there is very little
effective grit left after this period. So after 5 days has elapsed, it is time to check up on the contents of the barrel to see how things are progressing.
What to expect at this stage.
the barrel from the tumbler and take off the lid. Take care when doing this not to spill the contents - this is where your old newspapers come in handy or your paper towels. Remove the lid with the barrel
upright on a covered surface!
You should see that the water has turned thick and possibly creamy. It will be saturated with minute particles of reduced silicon carbide and equally minute particles of your
specimens. Basically it is muddy sludge, which is a product of the grinding process, and its color will be dependant on the rock you are grinding - a brown color for "tiger eye" or "citrine" for instance or a
blue-grey for most other rocks.
Dip your fingers in and remove a few fairly large pieces of rock, rinse them in a bucket of water, NOT DOWN THE SINK and decide whether they have the properties you are looking for
Examine them for :-
You can grind these out by continuing with this phase if you are not satisfied they have been reduced sufficiently to remove the outer flaws.
Ask yourself whether this is the final shape for your rocks, or are the corners too angular still? Do they need to be further rounded?
They may be flawless and have good shape - but are they the right size for
what you want to do with them when they are fully polished?
If you feel that the rocks need to stay in 80 grit for a longer period of time, then pour the content of the barrel through the 80 GRIT sieve and into the
bucket. NOT DOWN THE SINK! Swill the sieve around in the bucket to remove the mud and rinse the barrel out.
Replace the stones and pellets as they are into the barrel, and go back to