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## math/clay shrinkage question

### updated thu 27 nov 03 ### Maid O'Mud on tue 25 nov 03

I'm a left handed, left brained dyslexsic and need some help with math.

The clay body I use shrinks 11.5% (Tuckers Mid Smooth stone). This =
means that if I cut a 6 inch tile, the formula is 6 x .895 =3D 5.37 =
final fired size, right?=20

Ok, here's the question. I am aware that if I multiply 6 x 11.5% I will =
NOT get the right answer. The formula only works to get final =
shrinkage. I need to know what to multiply by so if I want a 6" =

Confusing enough? It took my poor husband a long time (years!) to =
explain that different formulas are needed - I just can't grasp how/why =
but accept it as fact.=20

Thank you

Sam - Maid O'Mud Pottery
=20
"First, the clay told me what to do.
Then, I told the clay what to do.
Now, we co-operate."
sam 1994
=20
http://www.ody.ca/~scuttell/

### Jim Kasper on tue 25 nov 03

Hi Sam,

100% - 11.5 % = 88.5 %
.885 x (original size) = 6"
thus

6"/.885 = original size

6.78" = original size
Regards,
Jim
> From: "Maid O'Mud"
>
> The clay body I use shrinks 11.5%
> Ok, here's the question. I need to know what to multiply by so if I want a 6" finished piece, what size I need to start with.

### Bruce Girrell on tue 25 nov 03

> I am aware that if I multiply 6 x 11.5%
> I will NOT get the right answer. The formula only works to get
> final shrinkage. I need to know what to multiply by so if I want
> a 6" finished piece, what size I need to start with.

A farmer has three cows and six geese. If the cows....

Oh, sorry.

I would set up the problem this way:
Let W be the length of the Wet piece and D be the length of the Dry piece
then

W - 0.115 x W = D

We can factor this to make the problem easier:
W x (1 - 0.115) = D or
0.885 x W = D

Note that the value is 0.885, not 0.895
if W = 6, then 0.885 x 6 = 5.31

All we have to do to work the other way is to solve the problem for the wet
length, W. To do that, divide both sides of the equation by 0.885:

(0.885 x W)/0.885 = D/0.885 <--- if that's confusing, ignore it

W = D/0.885

So if your dry length, D, is 6 inches the wet length, W, would be 6/0.885 =
6.78 inches.

Make sense?

Bruce "algebra R us" Girrell

### John Jensen on tue 25 nov 03

Six is to X (your plastic size tile) as 89.5 is to 100...6 times 100
divided by 89.5 equals your answer: 6.7 To check that multiply 6.7 by
.895.

John Jensen, Mudbug Pottery

### Steve Slatin on tue 25 nov 03

Dear Maid-o' --

Yes, and if you're in the mood to just do it, the formula you need
Is to DIVIDE by .0895. 6 divided by .0895 is 6.703910615.

You can test the accuracy of this by multiplying it my .0895, but you'll

probably see that the answer will be 6 (because you're multiplying and
dividing by the same number and that is the same as multiplying by one).

As a left handed no-brained dyslexic touch typist and once-upon-a-time
part-time editor, I consider it a privilege to help.

>I'm a left handed, left brained dyslexsic and need some help with math.

>The clay body I use shrinks 11.5% (Tuckers Mid Smooth stone). This
means >that if I cut a 6 inch tile, the formula is 6 x .895 = 5.37 final
fired >size, right?

>Ok, here's the question. I am aware that if I multiply 6 x 11.5% I
will >NOT get the right answer. The formula only works to get final
shrinkage. >I need to know what to multiply by so if I want a 6"

>Confusing enough? It took my poor husband a long time (years!) to
explain >that different formulas are needed - I just can't grasp how/why
but accept >it as fact.

>Thank you

### Donalson on tue 25 nov 03

I realize that Bruce's description of the formula and solution are =
absolutely correct. However, for those among us that continue to have =
difficulty with formula's etc., I offer the following link:=20

http://www.newsengin.com/neFreeTools.nsf/PercentChange/formPercentChange

This calculator easily does percentage decrease computations, which is =
just what we want, when we are looking for, the amount that clay =
shrinks. It does require a little bit of hunting and pecking to find =
the right answer, but that seems rather intuitive after using it a few =
times.=20
changes to 6 (the size of tile that Sam is after.. then that is an 11.5% =
decrease ( the amount that we know Sam's clay shrinks).=20
Play around with the first number and you see the effect that changing =
it has on the last number.....the percentage of shrinkage. The middle =
number (6) in this case, must stay the same because that is the size of =
the finished tile that Sam is after.

Hope this helps another person that gets dizzy when algebra equations =
are involved..

Craig AZ

### Hendrix, Taylor J. on tue 25 nov 03

Taylor, in Waco

-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of Bruce
Girrell
Sent: Tuesday, November 25, 2003 2:53 PM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: Math/clay shrinkage question

...
Let W be the length of the Wet piece and D be the length of the Dry
piece
then

W - 0.115 x W =3D D

... factor ...:
W x (1 - 0.115) =3D D or
0.885 x W =3D D

... value is 0.885, not 0.895
if W =3D 6, then 0.885 x 6 =3D 5.31

...solve the problem ...
... divide both sides of the equation by 0.885:

(0.885 x W)/0.885 =3D D/0.885 ...

W =3D D/0.885

So if your dry length, D, is 6 inches the wet length, W, would be
6/0.885 =3D
6.78 inches.

Make sense?

### Mary White on tue 25 nov 03

Okay, if the finished piece is 6" then 6" is 88.5% of what it was
originally. (100 -11.5=88.5)

So take 6" and divide by 88.5. Multiply the result by 100 and that's

If you want to test this, take your answer and type in - 11.5% on
your calculator and you'll get pretty close to 6". It's not exact, at
least not on my dinky little calculator, it's 5.99999.

Mary

>I'm a left handed, left brained dyslexsic and need some help with math.
>
>The clay body I use shrinks 11.5% (Tuckers Mid Smooth stone). This
>means that if I cut a 6 inch tile, the formula is 6 x .895 = 5.37
>final fired size, right?
>
>Ok, here's the question. I am aware that if I multiply 6 x 11.5% I
>will NOT get the right answer. The formula only works to get final
>shrinkage. I need to know what to multiply by so if I want a 6"
>
>Confusing enough? It took my poor husband a long time (years!) to
>explain that different formulas are needed - I just can't grasp
>how/why but accept it as fact.
>
>
>Thank you
>
>Sam - Maid O'Mud Pottery
>
>"First, the clay told me what to do.
>Then, I told the clay what to do.
>Now, we co-operate."
>sam 1994
>
>http://www.ody.ca/~scuttell/
>
>______________________________________________________________________________

--

### Gail Dapogny on tue 25 nov 03

Hi Sam,
You've gotten lots of answers that I suspect are all correct. But
since I am math-challenged as well, I will simply translate for you
the way I do it.

First of all, since you know that your shrinkage rate is 11.5%,
subtract that from 100 and you get 88.5.

size) and divide it by that above number (88.5) but move the decimal
point over two places (I don't know why). So, you are dividing 6 by
.885. It comes out to 6.779, rounded out to 6.78. In other words, just
slightly more than 6 3/4.

I keep posted a note to myself that reads:
finished measurement
divided by
100 minus shrinkage % or 88.5 ---- but make that
.885. **

(** Incidentally, 89.5 is NOT the correct number as subtracted from
100,. It's 88.5.)

Good luck! You will get it right.
---Gail

On Nov 25, 2003, at 8:48 AM, Maid O'Mud wrote:

> I'm a left handed, left brained dyslexsic and need some help with math.
>
> The clay body I use shrinks 11.5% (Tuckers Mid Smooth stone). This
> means that if I cut a 6 inch tile, the formula is 6 x .895 = 5.37
> final fired size, right?
>
> Ok, here's the question. I am aware that if I multiply 6 x 11.5% I
> will NOT get the right answer. The formula only works to get final
> shrinkage. I need to know what to multiply by so if I want a 6"
>
> Confusing enough? It took my poor husband a long time (years!) to
> explain that different formulas are needed - I just can't grasp
> how/why but accept it as fact.
>
>
> Thank you
>
> Sam - Maid O'Mud Pottery
>
> "First, the clay told me what to do.
> Then, I told the clay what to do.
> Now, we co-operate."
> sam 1994
>
> http://www.ody.ca/~scuttell/
>
> _______________________________________________________________________
> _______
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
>

### Sherrill Eatherly on tue 25 nov 03

1.First subtract 11.5 from 100 =88.5.
2.Then multiply 6 x.885 = 5.31.
3.Determine how much it is going to shrink, 6 minus 5.31 = 0.69
4.Add the .69 to the 6 which comes out to be 6.69 or rounded to 6.7".

Hope this helps,
Sherrill

----- Original Message -----
From: "Maid O'Mud"
To:
Sent: Tuesday, November 25, 2003 10:48 AM
Subject: Math/clay shrinkage question

I'm a left handed, left brained dyslexsic and need some help with math.

The clay body I use shrinks 11.5% (Tuckers Mid Smooth stone). This means
that if I cut a 6 inch tile, the formula is 6 x .895 = 5.37 final fired
size, right?

Ok, here's the question. I am aware that if I multiply 6 x 11.5% I will NOT
get the right answer. The formula only works to get final shrinkage. I
need to know what to multiply by so if I want a 6" finished piece, what size

Confusing enough? It took my poor husband a long time (years!) to explain
that different formulas are needed - I just can't grasp how/why but accept
it as fact.

Thank you

Sam - Maid O'Mud Pottery

"First, the clay told me what to do.
Then, I told the clay what to do.
Now, we co-operate."
sam 1994

http://www.ody.ca/~scuttell/

____________________________________________________________________________
__
Send postings to clayart@lsv.ceramics.org

You may look at the archives for the list or change your subscription
settings from http://www.ceramics.org/clayart/

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### Roly Beevor on wed 26 nov 03

Maid O'Mud wrote: I need to know what to multiply by so if I want a 6"

Sam

If you don't like formulas don't use them. My apologies if you know
perfectly well how to draw a line graph, but there certainly are people who
find this an even more frightening prospect than a formula. Lots of people
were put off graphs because you had to scale them at school to fit the paper
neatly, in this case you can use the actual size, so as long as you can find
a piece of squared paper at least 6" in both directions you have no
problems.

I would:

Get a piece of squared paper, and a pencil, and a ruler.

Mark one side "Before Firing" and an adjacent side "After Firing". Put a
spot in the corner between the sides you have marked, or if your squares go
all the way to the edge of the paper use the corner of the paper.

Measure six inches along the "Before Firing" direction, and mark; measure
5.37 inches along the "After Firing" direction, make your mark.

Follow the grid lines into the middle of the paper to the point where the 6"
before meets the 5.37" after, make another mark. Is this clear? I mean
draw a line perpendicular to the edge of the paper, from 6" on the before
edge, and another fron 5.37" on the after edge, to the point where they

Draw a line from (the dot in) the corner to the point you have just marked.
This line will go diagonally across the page.

Measure six inches along the after side and follow the grid from here out to
the diagonal line and back down to the before line. There is your answer,
six and a bit. To me its easier because I can see it and measure it. If
you have a pair of callipers or a stick you can mark you don't need to
measure.

Now you can relate any length final size to the appropriate length before
firing, as well as any starting size to the fired size, simply by following
from the appropriate length on one edge up (or across) to the diagonal line,
and, having turned through a right angle across (or down) to the
corresponding measurement.

If you pin the page to the wall you need never worry about the formula or
percent shrinkage, or the actual measurement again. Works so long as you
keep the same clay and firing temperature, no batteries, environmentally
friendly.

If the whole business seems too simple write "Analogue Shrinkage Calculator"
at the top.

Roly Beevor