We cannot emphasize enough the importance of proper labeling on containers of chemicals. The product may be completely harmless, but if the container is not labeled and its contents properly identified, how can you be sure of what you are dealing with? You not only have to think of yourself. You have to think of the other employee or student who might try to use what is in that unmarked container. All labels must be clear, written in English, and prominently displayed.

Primary Container Labeling: This is the label on the container we buy, or the original container. If the manufacturer's label falls off, a label of equal warning must be placed on the container.

Secondary Container Labeling: Any portion of a hazardous chemical moved from a primary container to a secondary container (i.e. spray bottle) must be labeled.

What about secondary containers in the science lab? Denison University says:

An important consideration on Denison's campus is when a compound is transferred into laboratory glassware. The glassware should always be labeled with its contents. Many times, hazardous solutions are left by laboratory workers with no label and therefore create risk to others in the lab. Also, when products of research are placed in vials or laboratory glassware, these containers should be labeled with their contents, dates they were made, and names of the researchers.
Stanford University says:
Anytime a chemical is used in a beaker or container other than one of the designated hot pots or baths at the wet benches, the following information must be posted nearby: