Silicone based adhesives are transparent and strong once dry, but can be toxic. [1] X Research source Aquarium glues fall under this category. Ultraviolet (UV) curing acrylic resins are excellent for repairing clear glass fragments that fit snugly together. They require exposure to sunlight or a UV lamp to set. [2] X Research source Opaque or colored glass may block some of the UV light, causing a weaker bond. If you are repairing an object that will be exposed to water, make sure the glue is waterproof. Most silicone adhesives and some UV resins are waterproof. If you are repairing an object that will come into contact with food or drink, check that the glue used is made for this purpose. Some adhesives are toxic even when dry.

Wear latex gloves while preparing and gluing the surfaces. This will prevent oil from your hands from rubbing off on the glass, and protect you from toxic or messy adhesives. Difficult stains can be scrubbed off using steel wool. [3] X Research source

UV curing adhesives require exposure to ultraviolet light. A few minutes in direct, bright sunlight or under a UV lamp should harden the glue. Allow more time for opaque glass or less intense sunlight. Silicone based glues require several hours at least to set. They do not require sunlight and will set in most weather conditions (5%–95% humidity; 40º–100ºF=5º-40ºC). [4] X Research source For large flat pieces of glass, fix them in place with a glass clamp or another clamp specialized for holding fragile objects. Avoid cracking the glass through over-tightening.

Both UV and silicone glues will dry completely clear, so the fracture should be well concealed.

Browse your hardware store or art supply store and read the glue labels to see which one is suitable for the materials you chose. A glue that dries clear is preferable for most art projects.

Wash the glass thoroughly with soap and water. Dry the glass with a clean paper towel. Empty some glue into a plastic container. This will make it easy to apply with a paintbrush, and cause it to dry slightly for a useful tacky consistency.

The setting time for the glue varies depending on the type of glue used. In most cases 5-10 minutes should be enough.

Wait another 5-10 minutes for this to take effect.

Apply, wait, and decorate each area in turn. Feel free to apply glue to a new area while you’re still decorating the previous one.