If you are wondering if you can mix two things, may I suggest a visit to the newbie section to learn more about what exactly our products are about in two posts I call what you need to know about making any product (part one) or (part two)? I've worked hard to create a section with all the basics you might want to know about our products, and I think it might be helpful for this question.
Lotion bars are what we call anhydrous products. Anhydrous means "without water". "An" means without and "hydrous" means water. Anhydrous products are those that contain only oil soluble ingredients and no water or water soluble ingredients.
What are water soluble ingredients? They are ingredients that contain water or mix well with water to form solutions. They are things that will dissolve or mix in water to create a uniform looking product. These would include things like water, alcohol, hydrosols, water soluble extracts (hydrolyzed proteins, vitamins, minerals, plant based things), powdered water soluble extracts (like green tea extract), and humectants (glycerin, sodium lactate, honey), to name a few.
the post on lotion bars:
What happens if you mix a water based thing into an oil based thing? You will get separation. Oil and water don't like each other (check your salad dressing to see this in action). If you add a water based thing - glycerin - to an oil based thing - shea butter - it will eventually seep out as the water and oil repel each other (this isn't exactly true, but it's easier to explain it this way...) If you really want to include glycerin into your product, you'll need an emulsifier.
Emulsification: What's that then?
Emulsification: A more in depth
The quick answer is that you can't add glycerin to an oil soluble lotion bar without an emulsifier.
Related posts on making lotion bars:
Newbie Tuesday: Let's make lotion bars!
Back to basics: The basic recipe
Back to basics: Lotion bars - tweaking the waxes
Back to basics: Lotion bars - tweaking the butters and oils
Back to basics: Lotion bars - let's get complicated
Back to basics: Lotion bars - wrap up and link-o-rama
The chemistry of our nails: Lotion bar with lecithin and lanolin