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easy measuring of specific gravity

updated fri 6 jan 06


Richard White on thu 5 jan 06

I've been lurking and learning here for awhile, and thought I would make my
first post as something to give to the group rather than ask of you (but
believe me, now that I've made the leap to joining, I'll be asking a-plenty...)

I'm just beginning to make some of my own glazes, and have read about the
importance of specific gravity as a measure of the proper slurry thickness,
but also have read about all the fun and games of trying to actually measure
it - baumes and hydrometers and pint jars and beer bottles... After some
head scratching, I came up with an easy foolproof "device" for precisely
measuring the specific gravity of my glaze mixes. It requires only your
regular scale which you use for weighing out the components of your recipes
(my instructions here are based on a triple beam balance, but you could
easily adapt the methodology for a digital one), a cheap plastic 10ml
graduated cylinder (a few dollars from one of the online home-schooling
science equipment supply houses, and get a plastic one so it won't break if
you drop it), a handful of ordinary steel washers from the bolt and screw
aisle at your local hardware store, and a few electrical zip ties (or
alternately, some duct tape).

First, set the scale for 90 grams and set the 10ml graduated cylinder on the
plate. By itself, it will not tip the balance, so add a few steel washers to
the plate until it begins to balance. Set a couple of the zip ties on the
plate too, and fiddle with it putting and taking washers (maybe try one or
two larger or smaller ones) until the combination of stuff is exactly 90
grams. When it balances, use the zip ties (or duct tape) to secure all the
washers together and then secure them all to the lower part of the graduated
cylinder. That's all the "construction."

To use it, simply set the balance weight to the 100 grams notch, fill the
graduated cylinder with your glaze mix to exactly the 10ml mark, and set it
on the scale platform. Now slide the 1 gram weight out the 1st beam until
the scale exactly balances, and simply read the number of grams of
additional mass that are shown. Mentally move the decimal point one place to
the left and add that number to one, and you now have the exact specific
gravity of the glaze mix in the cylinder.

An example or two may help those for whom numbers are not your favorite
subject. You have to slip the 1 gram weight out to 4.8 grams for the scale
to balance. The specific gravity, therefore, is 1.48. If you put 10ml of
your terra sig into the cylinder and had to slip the 1 gram weight out to
1.8 grams for it to balance, the S.G. of the terra sig is a perfect 1.18. If
the measured specific gravity is higher than you want, add a small amount of
water to your mix, stir well, measure out another 10ml and weigh it again.
If the specific gravity is too low, you'll need to do whatever is
appropriate for reducing the amount of water in that particular recipe (let
it settle and skim some water from the top or leave the bucket open until
enough water has evaporated, whatever your technique...) and then weigh
another 10ml sample in the specially-weighted graduated cylinder. As Chef
Tell used to say during his cooking show on TV (waaay back then...), "Very
simple, very easy, very quick."

Dick White
(there are 10 kinds of people in the world - those who understand binary and
those who don't...)

William & Susan Schran User on thu 5 jan 06

On 1/5/06 12:27 AM, "Richard White" wrote:

> After some
> head scratching, I came up with an easy foolproof "device" for precisely
> measuring the specific gravity of my glaze mixes.

Ok Dick, good to see you on the list.

Now, you homework is to bring one to class Monday.

-- William "Bill" Schran
Fredericksburg, Virginia

Richard White on thu 5 jan 06

nah, you can't have that one, but you can have the 100ml one I put together
at the same time... For anyone interested in the 100ml version, same idea,
but build the weighted empty graduated cylinder to exactly 100g. Then set
the middle beam to the 200g notch, and use the 10g beam and 1g beams
together to get your S.G. reading. From the previous example of 1.43 S.G.,
100ml of the glaze mix in the cylinder would cause a reading of 43 extra
grams at the balance point. I tried both the 100ml and 10ml cylinders and
found them equally easy and accurate, but for my personal purposes at home,
I like the smaller one because with a 100g or 200g test batch, I would
barely have enough in the whole batch to fill the 100ml cylinder, while 10ml
of slop is but a small squirt. In a larger studio setting mixing in 5 gal
buckets, the larger cylinder would be fine. I'll bring it with me.