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oldlady

Another Math Problem

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so tired after glazing and making things for a show on june 10.  and math is my least favorite thing and somehow the computer math things want to teach me how to do things instead of just  giving the answer.  so here i am again, begging for help.

 

question: what percentage is   .02 grams when added to 5 grams of glaze?  i just wanted to see what color would come out if i tried pansy purple and deep orchid to my clear glaze.

 

thank you for even considering answering this. 

 

 

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thanks, pieter, that makes it   4% ?

 

 

No, it.s 0.4%

 

Another way to do it if you have a calculator is to press the following keys:

 

5

x

.4

%

 

And you get the answer 0.02.

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Guest JBaymore

You are looking at 0.02 parts compared to 5.0 parts.  .02 / 5.0 = 0.004  Convert a decimal fraction to a percentage by moving the decimal point two places to the right....... 0.4%

 

best,

 

..............john

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I have a difficult time being that accurate with that small amount of glaze, always leave a % in the pan as a dusting. More power to you. . . . 

 

best,

Pres

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@ Lady, can't remember if your clear glaze has a fair bit of calcium in it? Is this the barium one? Anyhow, both those stains get the colour mainly by using chrome and tin, with a tiny bit of cobalt. For the purple to develop the glaze must have whiting somewhere between 12 - 15% (or wollastonite and whiting supplying the calcium). If you're not sure you can get a quick idea if the stains will turn out purple by just dipping the tip of a wet paintbrush into the stain and doing a swipe on top of your glaze. If it comes out purple then do the fiddly little glaze tests. (also no zinc in the glaze, which I don't think you use anyway so no worries there)

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Guest JBaymore

I have a difficult time being that accurate with that small amount of glaze, always leave a % in the pan as a dusting. More power to you. . . . 

 

best,

Pres

 

Unless you have a REALLY good scale........ anything less than a 100 gram test batch is open to HUGE plus or minus errors.  If you are using a triple beam ....everything is plus or minus one tenth of a gram.  If you are weighing four tenths of a gram........ to put into a 100 gram batch... the amount of material you have in the scoop will be somewhere between 3 tenths to 5 tenths of a gram.  You have no idea where.

 

best,

 

..................john

Edited by JBaymore
HUGH changed to HUGE. . . pres

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thank all of you for your concern and advice.  when i use my Ohaus triple beam i hope i am reading the small scale at the bottom correctly.  i have it in place where it is level.  sharpie outline on stainless table gets it right every time.  the amount of glaze i test for color only is about 1 tablespoon.  the large bucket of base glaze makes taking one spoonful out not such a big deal.  it is actually a stainless spoon i got from a thrift shop but it contains just about 5 grams.  the 5 gram is easy to see.  and i am careful to read the horizontal line correctly.

 

now the part i have begun to doubt.  the lines between 0 grams and 1 gram.  i put the pointer exactly on the second line.  that amount is what i now question.  i think it is 2 tenths of one gram. but i wrote  .02.   am i right?

 

that amount fits neatly on the curved end of one of my kemper tools that has a pointed arrow-like end and the curved pointed end.  remember, i am only trying to see whether the colors i have work in the base glaze.   if the color is there, then i might do some more testing with larger amounts.    yes, Min, you are right, the zinc free barium one.  (only 8% barium, those of you who worry.)

 

my biggest problem with using 100 grams as a color test is that i cannot find a way to overcome my Scots heritage and waste more than 95 grams of glaze.  so my 8 foot long stainless glazing table is covered with the dead bodies of about 50 ugly 100 gram tests that have been accumulating for years.  

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I bought a good digital scale to do 100 gram tests and then I mix up a 1000 gram test if I like the glaze just to make sure it works in a larger batch.  The 5 gram test Old Lady was asking about blew my mind.  Denice

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sorry, denice, it is easy if you have a bucket of DRY base glaze.  i am only testing to see if my colors work.  the glaze is wonderful.

 

min, i have just added you to a conversation where i gave the recipe.  hope you get it and understand it is maybe easier than typing out the whole thing.  thanks for looking at it.

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Guest JBaymore

The smallest marking on an OHaus triple beam are marked in 1/10th gram markings ...that is the lowest bar on the front.  The full length of the bar totals 10 grams....... calibrated in 1/10th gram measurements.

 

BUT.... the accuracy factor for such a scale (in totally good repair and used 100% properly as to sight line on the balance lines, being totally level, and having the knife edge on the balance point in good condition) is plus or minus 1/10th of a gram.  So for example if you weigh out 1 gram in the pan according to the scale.... you have anywhere between 9/10th of a gram and 1 and 1/10th of a gram.  No way to know where you are there.  Could be anywhere within that range.

 

If you are weighing a total batch size of 100 grams of total material........ that level of inaccuracy... 1/10th of a gram is a tiny percentage of error.  0.1/100=0.001=0.1%  So you have a 1/10th of a percent potential error in the weighing.  For most of what we do..... insignificant.

 

If you are weighing only 5 grams of material as a total....... then first of all.... you have anywhere between 4.9 grams and 5.1 grams.  Again.... you have no idea how much.  THEN........ the scale error factor at the level of a total batch of only 5 grams is a whopping 2%. 

 

The smallest amount that you can even weigh with ta triple beam is 0.1 grams.  And at that point you have anywhere between nothing at all and 0.2 grams of stuff.  You are totally into the realm of pretty useless.  The error factor on trying to weigh out 1/10th of a gram is anywhere from 100% to infinity.

 

100 grams is the minimum for an anywhere near accurate level of a test batch of a glaze.  1/10 of a percent is a good accuracy for testing.

 

You can get digital scales that are accurate to 1/100th of a gram.  They'll drive you nuts if you are using local pickup ventilation........ because the airflow will cause the readings to jump all over the place.

 

If I understand what you are saying above ...  it sounds like you are scooping 5 grams of LIQUID glaze out of a bucket.  Is that correct?  If so... you don't have 5 grams of glaze materials there... you have X grams of dry materials and Y grams of water.  The amount of dry materials in the amount of liquid material is based on the Specific Gravity of the wet mixture.  It will always be less dry material than the total weight of the liquid.  So if this is what you are doing... you are dealing with apples and oranges.

 

Hope this helps.

 

best,

 

.....................john

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Oldlady, with your askance.

 

John-

I think that the inaccuracy really isn't so much of an issue for Oldlady, since she is only trying to determine whether a particular addition will work as a coloring agent in her base glaze. If it succeeds at all, I would assume that she would then use a larger batch of base to do a progressive line blend to find an optimum amount of additive to achieve the specific color saturation/value she desires.

Respectfully submitted for your consideration,

Fred

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Guest JBaymore

Correct to a degree, Fred.  And respectfully acknowledged.

 

But.....................

 

Let's say that you want to see if colorant A gives you some nice color.  You do the test the way it is described.  It comes out bubbly black.  You reject the result as nothing that you'd want.  Turns out that colorant A is cobalt oxide.  Turns out the percentage added if checked accurately was maybe 7% by weight.  Yup.... bubbly black.  BUT... if the test had way less than that amount..... it'd be various shades of blue.  That possibility would be missed if all that was done was the "quick and dirty" test.

 

Some colorants produce very different color renditions in different percentages.  Take iron....... celadon to temmoku.  Manganese........ tans to black.  Copper.... greens to black.  And so on.

 

best,

 

....................john

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John-

Definitely agree with your assessment with the examples you give. Especially as it pertains to less experienced glaze experimenters in color development. I was presuming, perhaps wrongly, that with oldlady's experience she could glean reasonable results from her methodology, without the need to be overly concerned about a +/- 2% inaccuracy.

Option amended with embarrassment for forgetting the vast expanse of experience within the readership.

Fred

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thank you, john and fred.  i have been making glazes for years but only ones that i have been given recipes for.  no math, no chemistry.  just surface results and colors.  recipes that look good on brown clays look insipid on white.  so i have whittled down the number of base glazes.

 

the base glaze is dry.  whenever i go to the trouble of making a glaze that i have proven a good one for my work, i do a full bucket, about 10,000 grams.  then i mix it thoroughly with a mechanical mixer for many minutes with my respirator on and all of this is done outside with a fan.  yes, i may lose a few tiny bits to the wind.  that bucket can last a very long time except for the base glaze that i use to do green.  which is copper carb.

 

the colors i am testing are from mason stains.  i have about 20 containers of colors.  they are made with ingredients that may react badly or not at all with my base glaze.  i am just trying to see if i can get ANYTHING from a particular color.  i test all glazes to be sure that i like the way the glaze works on my clay.  then i try the colors to see if i can get some variety.  i have friends who can get wonderful crimson.  not me.  not on white clay.  wish i could.

 

my main concern is that i texture nearly everything.  when you are using a responsive clay, little loafers is a white stoneware without grog, any mark shows up on the final piece.  similar to the use of porcelain which can show fingerprint ridges, my clay allows me to use very fine leaves, no thicker than a thin sheet of paper.  so when i found a clear glaze that meets all my requirements, i was very excited about it.  now i want to see how, yellow (good), blue (good), pink, purple, and various other things will look in that base.

post-2431-0-22819700-1496254115_thumb.jpg

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Guest JBaymore

Option amended with embarrassment for forgetting the vast expanse of experience within the readership.

 

No reason to be embarrassed at ALL, Fred.  I just tend to always think of the huge CAD membership that might be reading various threads when I see and possibly put stuff posted on here.  Sometimes that leads things off on a bit of a tangent.  There is a core group that is very involved and posts often.  But there is a very large number of members (and visitors) that simply read the forums without really making their presence known  (number of members is at over 21,000 now).

 

best,

 

........................john

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Guest JBaymore

 

the colors i am testing are from mason stains.  i have about 20 containers of colors.  

 

For just a "will the base glaze chemistry kill the color" answer with stabilized glaze stains like these ........ what you are using as a starting place is gonna' work basically fine probably 95% of the time.  These are mainly suspension colors ...so color intensity will change with percentage additions... but not much else. 

 

Not many people dry mix the batches like you describe and keep it dry.  Thanks for the added info.  That takes out the swet versus dry thing I mentioned above.

 

best,

 

......................john

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thank you, john.  of course, in the area of testing glazes my method of color checking would be silly.  i appreciate your thoughtful answer and know the responsibility you feel to make sure casual readers do not think the forum answers are written in stone, approved and signed by you.

 

i hope i do not mislead anyone into thinking that what i do will work for them.  but it really is hard not to say TRY IT, WHAT DO YOU HAVE TO LOSE, IT IS ONLY CLAY.

 

i have edited the first posts to show the base glaze is dry.

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If you know the volume and weight you can estimate how much dry material is in the glaze.

 

A little more maths

(Weight of glaze - Volume of glaze) x (5/3) = Dry glaze

 

Example, 50ml of glaze that weighs 75g (specific gravity 1.5) you have (75-50) x (5/3) = 41.7g dry glaze. 1% additions are 0.4g but if you need to get lower I would try a line blend from 0-1%. I think it is probably the fastest way to have a base glaze and test colourant additions.

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now the part i have begun to doubt.  the lines between 0 grams and 1 gram.  i put the pointer exactly on the second line.  that amount is what i now question.  i think it is 2 tenths of one gram. but i wrote  .02.   am i right?

 

 

The first figure after a decimal point represents *tenths* - the second figure after a decimal point represents hundredths.

 

0.02 is two hundredths, or as a fraction it's  2/100  -    two tenths would be 0.2   -  or 2/10 as a fraction

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thank you ayjay.  so i should have written   0.2.   thank you.  ( is it 4%?)

  0.2  is  4%  of  5.0

 

Use a calculator  - divide 5 by 100 = 0.05 - (so 0.05 is 1%  of 5) multiply 0.05 by 4 = 0.2

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