I have done some tests on the effects that water and other ingredients have in crafting new materials:
Milk of Lime
17.23/32.15/17.46/33.17 Lime
16.02/34.23/25.06/24.68 Water_1
16.03/34.21/25.00/24.77 Milk of Lime (1:100)
Conclusion: Water has 100x the weight as the Lime. Lime purity does not matter.
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Baking
21.04/43.35/19.99/15.63 Flour
15.83/34.26/26.21/23.70 Water-2
18.44/38.81/23.11/19.66 Pie Dough (1:1) 35 Flour, 75 Water
18.44/38.81/23.11/19.66 Oatmeal Cracker (1:1) 25 Flour, 75 Water
Water Purity affect baked goods like it always did, except now it's not a flat 25. Water exists as a single ingredient.
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Limed Hides
31.41/38.41/14.18/16.00 Hide-1
30.85/36.30/13.49/19.36 Hide-2
16.03/34.21/25.00/24.77 Milk of Lime
23.73/36.31/19.59/20.38 Limed-Hide-1 (1:1)
23.45/35.26/19.24/22.06 Limed-Hide-2 (1:1)
Milk of Lime and the Dried Hides combined in equal strength, just as in all Crafting Recipes.
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Tanning Fluid
31.41/38.41/14.18/16.00 Brain-1
15.93/33.98/29.56/20.53 Water-3
16.66/34.19/28.83/20.32 Tanning Fluid 5% (1:20)
30.85/36.30/13.49/19.36 Brain-2
17.34/34.29/28.10/20.27 Tanning Fluid 10% (1:20)
The contents of the Bucket, whether Water or 5% Fluid, have 20x more weight in the combination than the Brain.
Brain Purity is largely irrelevant.
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Leather
23.73/36.31/19.59/20.38 Limed-Hide-1 (1:1)
23.45/35.26/19.24/22.06 Limed-Hide-2 (1:1)
17.34/34.29/28.10/20.27 Tanning Fluid 10%
15.80/34.24/27.51/22.46 Water-4
23.73/36.31/19.59/20.38 Leather-1
23.45/35.26/19.24/22.06 Leather-2
Leather Purity is IDENTICAL to that of the Limed Hide. Tanning Fluid has NO EFFECT
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For the two "Fluids" water vastly outweighs and overpowers them in purity effect.
The worst-case scenario of putting a 0/33/33/33 Brain into 100/0/0/0 water only results in 95/1.6/1.6/1.6, which is has an 8.89x multiplier.
Water is by and large THE MOST IMPORTANT INGREDIENT. Given the interactions with clay and clay pots, it will likely be the linchpin of purity grinding.
update: Harvested my leather, so that info is added.