Making Casein Glue from Milk
This recipe can be used to make a paint binder or gesso adhesive. It will give you about 2 ounces of glue.
1. Non-fat (skim) milk, 4 ounces (@ 1/4 cup)
2. 1-2 glass jars or bowls that hold 4-6 ounces, & 1 ceramic or aluminum
pan for heating
3. Distilled white vinegar, 1 ounce (2 tblspns)
4. Paper coffee filters, small metal strainer, paper towels, sticks for stirring
5. Distilled Water, 1 ounce
6. Borax, ½ tsp
7. Small 2 ounce jars
Procedure:
1. Pour the milk in a jar and let it warm to room temperature.
2. Add the vinegar. This will coagulate the milk protein into small lumps
(curdle) as it begins to precipitate.
3. Pour into pan and heat the solution on low (@190°F) for about 5-10
minutes stirring occasionally until the liquid becomes fairly clear, and the
curds group together.
4. Remove the pot from the heat and allow the curds to completely settle for
another 5-10 minutes.
5. Place a coffee filter in a strainer over the top of a jar or bowl and slowly
pour the curds into the filter. You'll wind up with @ ½ cup liquid
which can be discarded. The remaining solids will be @ 1 teaspoon.
6. Gently press the curds in the filter to squeeze out excess liquid. Place
the curds on a paper towel. Break down the large lumps into smaller pieces.
7. Scrape the curds into an empty jar.
8. Heat about 1 oz of water below boiling point (microwave on high @ 22 sec.)
and add borax powder. Stir briefly until dissolved.
9. Slowly add about half of this solution to the curds while stirring in order
to neutralize any remaining acid from the vinegar. Let it sit for about 4
hours, stirring occasionally. The white curds will slowly dissolve and turn
into a somewhat translucent glue. Add more borax liquid if it's still too
lumpy, or make more curds if it's too thin. You can dilute the glue by just
adding water.
Notes:
Use fresh (unfortified, non-homogenized) pasteurized non-fat cow's milk, if
you can find it. Most commercial brands add vitamins A & E (D comes from
UV light) and emulsifiers. Check with local dairies in your area or farmer's
markets. Otherwise, look for powdered non-fat milk also without additives.
What if any risks those additives may have on the paint or surfaces I can't
honestly say, but it's not needed so it's worth the extra effort to find it
fresh. You could also use cheese instead of milk; but there are added enzyme
and bacterial cultures to deal with, so I think milk is a better choice.
Borax powder (sodium borate) can usually be found in most grocery stores in the laundry section. It's made in different levels of hydration, from 20 "mule" (laundry) down to 0. The borax sold in pigment supply stores is around 5 mule. I haven't found that it makes much difference which I type I use, but the higher grade (lower mule number) may dissolve better. Borax should not be inhaled or ingested, and can irritate the eyes, so be careful with it.
Other things can be substituted for borax, like tri-sodium phosphate (TSP.) This can be found in hardware stores in the janitorial section, but is banned in some areas because of the phosphate content. It seems to work well and breaks down the curds fast, but is typically more expensive by volume than borax. Other things to use are baking soda, ammonia carbonate, or hydrated lime all diluted in the same proportions as the borax solution above. Baking soda seems to make a weaker glue, and ammonia is very acidic. Lime reportedly makes a stronger glue but a milkier paint, and can adversely affect some pigments.
-DBC