Clays can be used by themselves or with added ingredients as facial masks.  If you are just using clay, you would mix it half and half with the liquid of your choice.  Each clay has different properties which you may want to take into consideration when you are creating your masks.  French Green Clay, like the Moroccan Red, is efficient at drawing oils from the skin. Use this clay for oily skin. Kaolin Clay (or China clay or white clay) is one of the mildest of all clays and can be used on even the most sensitive skin, and because it doesn't draw oils from the skin it can be used on the driest skin types.  This is clay is also used in face and linen powder. Pink clay is mild clay that can be used everyday without drying skin.
If you will be selling your products and you want to keep as natural as possible you should just sell the dry clay with instructions, otherwise if you add your moisture to your clay you will have to use an acceptable preservative, which means a synthetic preservative. 
You can use these liquids for normal to dry skin:
distilled, spring, or mineral water
milk or cream
honey
vegetable glycerin   
floral hydrosols
cooled herbal teas
cold pressed oils
essential oils: lavender, chamomile, rose geranium, jasmine, and patchouli.
For oily or problem skin:
yogurt
buttermilk
Apple cider vinegar
witch hazel
vodka
honey
orange flower water
herbal vinegars
aloe vera gel
cooled herbal infusions
essential oils for dry skin: rosemary, eucalyptus, peppermint, thyme, lemon verbena, cedarwood, petigrain, lemongrass, sage.
essential oil for blemished acneic skin: eucalyptus, thyme, tea tree, juniper, cypress, pine, fir, and lemon.

There are several ways of making milk soaps, I have included two. 
Some things to remember when making a milk soap:
Milk soaps will heat up so don't use a light weight plastic mold. 
For the first week or more you milk soap may smell like ammonia, this is completely normal, it will disappear.

I was very lucky, I found some condensed goat milk. But you can use any canned condensed milk.  I shorted my recipe by the amount of condensed milk I was going to use and added the canned goats milk at trace.  Keep in mind that if you  short your water, you trace will speed up, so be ready with all of your ingredients ahead of time.

Clays

Clay gives soap a smooth creamy lather and can be used to dry oily skin or in a shaving soap. Clay can also be used as a natural colorant.  Depending on the clay use it at a rate of 1 teaspoon to 1 Tablespoon per pound of soap.

Clay: Bentonite

Bentonite clay is commonly used in shaving soaps to make the razor slippery to avoid cuts to the skin. 

Clay: French Green

French Green Clay, like the Moroccan Red, is efficient at drawing oils from the skin. Use this clay for oily skin.

Clay: Fullers Earth

Fullers earth has a type of silicone in it and makes the best clay to use when making a shaving soap. It is also a good facial clay for oily or scaly skin types.  Add 1 Tablespoon per pound of soap

Clay: Kaolin 

Kaolin Clay (or China clay or white clay) is one of the mildest of all clays and can be used on even the most sensitive skin, and because it doesn't draw oils from the skin it can be used on the driest skin types.  This is clay is also used in face and linen powder.

Clay: Moroccan Red

This clay is a strong cleansing clay that will draw oils from the skin, so it may not be a good idea to use this clay if you have normal to dry skin. 

Clay: Pink

Pink clay is mild clay that can be used everyday without drying skin.  You can also add a bit of this to your body powders to make a lovely pink body powder.