Products sold in small quantities may not be readily visible, as they can coat the bottom or walls of the vial. When stabilizing your product, it's important that you ensure that the solvent comes into contact with all areas of the vial. Read on to learn more. Freeze-dried products often cause concern as they are sometimes difficult to see with the naked eye. Typical freeze-dried products that you often expect to see are shown in the first example below. The vial on the left depicts a dyed example of a product and the vial on the right is an undyed product.
In this case, it is easy to see the product in the bottom of the container. However, freeze-dried products can also resemble a smear around the vial. The second example below shows several ways these products can be distributed around a vial. The left and middle vials are examples of a dyed product, which makes the process easier to visualize, and the vial on the right (an undyed product) demonstrates how, although the product is present, it may appear invisible.