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Reclaiming oil from slab saw residue?

This is a question for the Lapidaries:

When I change the gravy thick gunk from my slab saw, I would like to
reclaim any of the oil from the rock particles.

I don’t like to throw something away that might have some value -
like the cutting oil that I bought to refill the saw was about $20
per gallon.

Are there special ways to separate the oil from the rock dust?

Larry E. Whittington

Hi Larry,

A cost effective and efficient method is to set up a filtration
system from scrap. You need a length of 4 - 6" pvc drain pipe,
(diameter is dependant upon the diameter of the toilet paper rolls
to be used), around 24 - 30" long, a cap for the bottom of the pipe,
a plastic or metal drum for the head, usually around the 5 gallon
capacity and some scrap wood to fabricate the stand. Cut/Drill a
4-6" hole in the base of the drum, insert the uncapped end of the
filtration pipe, ensure it stands a little proud of the base of the
drum as some of the rock particulate will settle out in the drum
before entering the filtration, seal the entry point with a suitable
adhesive, plumbers mastic works a treat, insert 3 - 4 toilet rolls as
the filter, you will need a further rod or tube or suitable cap to
seal the otherwise 2" toilet roll hole. Drill a 5mm hole in the base
cap of the filtration pipe and mount the assembly on the frame with
enough height to allow your collection drum/tray to stand underneath.
If the base cap is not a threaded fitting then you will have to glue
the base cap to the filtration tube or support the base of the
filtration tube, a couple of 6" nails driven into the frame
supporting the basecap is usually adequate. Pour the cutting oil
into the top drum and allow gravity & time to work.

Kind regards
Don Iorns

When I change the gravy thick gunk from my slab saw, I would like
to reclaim any of the oil from the rock particles...Are there
special ways to separate the oil from the rock dust? 

Yes but my method is messy and time-consuming. You’ll need a large
brown paper grocery bag or two, a large metal screen that will fit
over an adequate-sized container to catch the oil, and a place to
store the whole shebang for the time needed for the process.

I usually put one big paper bag inside the other, and trowel the saw
sludge into the bag (after setting it atop the screen which is atop
the plastic bucket or whatever). The fine rock dust that makes up the
sludge will eventually release the oil into the container via
gravity. If you can allow 3 or even 4 months for the process that’s
ideal. The longer it sits, the more oil you’ll salvage. The grocery
bags function as an excellent filter. The residue is very clean and
nearly oil-free.

When I’m doing a lot of sawing I have enough oil on hand to keep the
filtering process going continuously while having enough fresh oil
to keep the saw filled all the time.

Rick Martin

It’s been a decade or so since I saw my father do this so I’m hazy on
the details, and he’s deceased now so I can’t ask him. But I believe
he strained the oil through several layers of either cloth or paper
towels using an old coffee can to catch the strained oil.

Kathy Johnson
Feathered Gems Jewelry


Years ago when we were using Almag. Pella and some of the other
oils, it was fairly easy to just put the gray gunk into a brown paper
bag, hang it over a 5 gal can and let it filter through. Almag and
others are still out there but very expensive for my taste. I
currently use KoolKut from Graves Co. which is a ultra-refined
mineral oil based lubricant. It is also fairly expensive but does a
great job and has no odor or lasting oily residue. It washes away
with water and a little de-greaser. Unfortunately, KoolKut is all but
impossible to recover. It just doesn’t seen to like separating from
the rock dust/particles. About the best you can ask for is let it
settle in a bag or bucket for a few days and recover the top few
inches after the heavy stuff settles out.

Good luck and cheers, Don in SOFL


That’s not so difficult. I did a story about it some while

one arm Hans in Moncton Canada


Strain your oil into a clean bucket through a brown paper bag. The
bag acts as a coffee filter for your oil. You may need to repeat.

Karen Bahr - Karen’s Artworx
Calgary, Alberta, Canada

I take 1/2 inch diameter PVC pipe and cut it 4 or 5 inches long and
stand the pieces up in a 5 gallon bucket until the bottom is full.
This looks like a honeycomb and gives a place for the oil to drain
into. I place a paper bag in the bucket on top the PVC pipe. I then
scoop the sludge into the bag. I fold the top of the bag over and
put the lid on the bucket. I have several saws so I stack these
buckets until I change the oil again. When I change oil again I pull
out the now dry paper bag of rock dirt and throw it away. I pour the
filtered oil into an empty bucket clean the sludge out of the saw and
fill with the filtered oil.

John Daly

The method I’ve used, and other amateurs I know, is just to filter
it through a paper bag into a bucket. Or two buckets - one on top of
the other, the top one with the paper bag and lots of holes drilled
in it.

It seems to me that professional slabbers must have better methods
available. As you say, the stuff is too expensive to throw out.

Al Balmer
Sun City, AZ

John…Neat idea of the honeycomb!!! Never used that before but
sounds like a great idea. I’ll try it too! Never too old to learn
are we??

from Don in SOFL

A little late replying to this thread but I use mineral oil and when
I want to “filter” it I just drain the holding tank into 2 or 5
gallon buckets, let it set for a day or so and pour off the perfectly
clear oil as the sludge is heavy and always settles out. I can
reclaim almost all of the drained oil leaving only the bottom sludge
to sieve through a bag. Works simply and well and I have only gone
through about 5 gallons of mineral oil in the last 4 years or so. I
would not use anything but mineral oil and this makes it affordable.