[Strawbale] Milk Paint & Priming

[Athena & Bill Steen]

> Hello-
> Anyone have any milk paint recipes to share?  I've come across some
> that call for curdling the milk and some that don't, as well as some
> calling for linseed oil (and some without).  I'm looking for a simple
> recipe for walls & ceiling.  Also any recommendations on priming
> sheetrock prior to using milk paint?
> Thanks.
> Tom
>
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Tom,
Here is the process as described in a handout that is part of our  
Artistry with Clay and Lime Workshop.

Bill
Athena & Bill Steen
The Canelo Project
HC1 Box 324
Canelo/Elgin, AZ 85611
absteen at dakotacom.net
www.caneloproject.com


Casein Paint from Curds (quark)
and Lime Putty
Traditional recipe by weight
This recipe which involves making the
curds from non-fat milk is obviously
more troublesome than using casein
powder but since it is the classic way of
making the paint let’s being with it. It’s
good to remember that the first time one
makes this paint it will seem challenging
and it is easy to get discouraged.
However, having gone through the
process once or twice it will be much
easier.
20% curds (quark)
5% lime putty
75% filler
1/3-liter water for every 1 kg of filler.

Making Curds (Quark) and Lime Putty
- Non-fat milk can be left to sour by
leaving it in a warm place for several
days. Try to collect the curds right
when they have formed, otherwise
they will become tough and stringy.
Using lemon juice or rennet will
make the curds more acidic and they
will need to be washed thoroughly
before using them for paint. The
curds can be hung in a linen cloth or
cheesecloth to let the excess whey
drain off.

- Lime putty can be made from Type S
lime (dry powder), available at any
building supply store. The dry
powder can be added to water until
toothpaste-like consistency is
achieved. A bag of lime will be way
more than is needed for making
small quantities of paint. One bag
typically will make 3 – 5 gallon
buckets of putty while only
tablespoon quantities are needed for
paint. Store it for later use as plaster
or give some to friends. As the putty
settles there will be a layer of water
that forms on top, this layer is
referred to as limewater and is an
ideal water to mix pigment with for
painting fresco.

Making the Paint
- For the curds to achieve a binding or
adhesive quality they need to be
combined with the lime putty. A
ratio of 20% curds to 5% lime putty
is an approximate guideline and
doesn’t need to be exact. We’ve
found that one of the easiest ways to
do this is in a blender. It might be
necessary to add a little water, but try
first without it. Strain the mix when
finished to remove any lumps and
wash the blender immediately
because lime-casein when it dries is
difficult to remove. Acquiring an
inexpensive blender that is dedicated
to making paint is not a bad idea.
The mixture of casein and lime
should have a viscous consistency
and should be mixed into paint as
soon as possible otherwise it has a
tendency to gel. Then add the
designated amount of water to the
casein-lime.

- Prepare the pigments by crushing
them with a rolling pin. A plastic
cutting board makes a good surface
to do this on. Again, it’s a good idea
to have ones that are dedicated just
for making paint. Grind until all the
lumps have disappeared. It might be
helpful to dampen the pigment
slightly.
- Add the ground pigment to enough
of the casein-lime-water until it’s
thoroughly dispersed and then add
the remaining amount of liquid.
- In the case of an opaque paint, fillers
and pigment combined will represent
approximately 75% of the mix by
weight. The most common filler
used in casein paint is chalk or
whiting. It is available through
suppliers of artist materials or
ceramic supply outlets. The ratio of
pigment to filler will be determined
by the color that is desired. Smaller
amounts of pigment with higher
percentages of fillers equal less
intense colors. This will take a little
experimentation, as it will vary
depending upon the pigment that is
used.

- To make a wash rather than a solid
covering paint, simple reduce the
amount of combined filler/pigment.
Since that will increase the
concentration of casein, the water
must be increased. Test to see how
much water can be added without the
paint dusting.
*As an exercise let’s work through the
formula listed above. And let us assume
that the filler/pigment that represents
75% of the mix weighs 1 kilogram or
1000 grams. If that 1000 grams
represents 75%, then for the casein-lime
binder to complete the additional 25%
would need to be 333.3 grams. We also
know that for every 1 kilogram of
filler/pigment 1/3 liter (333 ml)(10oz) of
water is needed. Additional water can
be added as needed to achieve the
desired consistency.

The following proportions by volume
will give pretty close to the same results
- 1 part casein-lime binder, 3 parts
filler/pigment and 1 part water.
Test samples will indicate if any
adjustment is needed. For example, the
paint may need some additional water to
spread easily, additional binder if it dusts
or additional filler/pigment if it is too
thin. Remember, casein paint will
appear somewhat transparent when it’s
painted, but opaque when it dries.