Specific Gravity from Dry Ingredients?

[kraythe]

Greetings, 

I already know the basics of SG if I have a measure amount of glaze and the amount of water. But what if all I have are dry ingredients?  Lets say I have a dry glaze that I have planned out. I want to make perhaps 200g of it to make a small batch for testing, is there any way I can know exactly how much water to use in order to get a specific gravity of 1.45 for pouring (since I wont have enough to dip) on test pieces. As my understanding goes the SG is the weight of the water + the weight of the mass of ingredients. So my thought is that if I am going to have 200g of ingredients and then I would need 80 g by weight of water to hit the target SG. Is that the case? If not how can I hit the right SG from dry measure to wet.

thanks in advance. 

[Tyler Miller]

An algebraic reworking of Brongniart's formula (google will provide a better explanation than I) will get you there.  You will need to know the SG of the dry mix of materials you have in order to get there.

[Min]

Think you are making this more complicated than it needs to be. Just mix it up with a minimal amount of water, like just enough to make a thickish slurry, get your SG and add water as necessary. A lot of this is not rocket science, it's just doing some testing. 

[dhPotter]

Calculate 3 ounces of water per 100 grams of dry material. Then use a few ounces less so you can add if need be. 

 200 grams calculates to 6 ounces of water. Use 4 ounces to start, then make adjustments. 

 

[Joseph Fireborn]

I am with Min. Just record the amount of water you add and the amount of dry materials you add. When the slurry starts getting close to where you think it is right. Check SG. Then you will have your ratio. It is as simple as that.

 

[High Bridge Pottery]

Googling Brongniart's formula a clay art post comes up first. Can you take this bit and say in a liquid of 1.5sg ~ 1 water : 1.25 dry material. That would mean to get a volume with 1.5sg you would need 200 dry for 160g water. Maybe it doesn't work, not sure. The volume part is confusing me.

So, for example, suppose that a liter of your glaze slop weighs 1500 g. 

Then the amount of dry material in it is (1500-1000)5/3 = 833.3 g dry matter 
per liter. And since the total slop mass is 1500 g, we also know that the 
glaze slop contains 1500-833.3 = 666.7 g water per liter of slop. 

[dhPotter]

I like the word slurry better than slop. 

People slop hogs.

[Tyler Miller]

Joel,

if you have a target specific gravity and desired volume, you should be able to figure out the weight of the glaze you want to make for your desired volume.  With this you can figure out how much dry material (of a known specific gravity) you need, and then adding water to your target volume should be easy.

Edit:  It's also a useful formula if you should ever find yourself in a place where you're in a postion to steal the recipe of a traditionally formulated Japanese glaze