Grind the milk thistle seeds to a coarse powder. This may need to be done in batches.
Pour the resulting powder into a jar.
Combine the vegetable glyerine and water in a measuring cup and stir well.
Pour the glycerine mixture into the jar, making sure that at least 2 inches of liquid covers the ground seeds.
Stir the mixture thoroughly.
Cap the jar tightly and shake well.
Store the jar in a cool, dry spot away from heat and light for two to four weeks. Shake jar once or twice daily during this time.
Allow the herbs to settle to bottom of jar by not shaking for one to two days before straining.
Place mesh strainer over the mouth of another jar and line with cheesecloth.
Gently pour the infused liquid through the strainer and into the second jar.
Place wet pulp in cheesecloth and squeeze to extract the remaining liquid.
Cover tightly and store in the refrigerator or in a cool, dry, darkened area.