What Is a Brick Frog? And How It Helps Identify a Brick

A brick frog is a depression or recess formed in one face of a brick. Not every brick has one, and frogs vary considerably in shape, depth, position and markings. When present, the frog can be one of the most useful physical clues when researching an unidentified brick.

Why do bricks have frogs?

Frogs have historically been associated with the manufacture and handling of bricks and can reduce the amount of material in a brick while retaining useful shape and strength. The exact manufacturing reason varies by brick type and production method. The important point for identification is that the frog forms part of the brick's physical design.

What should you photograph?

Take a photograph showing the entire face first. Then take a close-up of the frog and any lettering or symbols inside it. Include enough surrounding brick to show the frog's size and position. A cropped photograph containing only a few letters can remove information that distinguishes one mould from another.

Maker's marks and mould codes

Bricks can carry names, initials, numbers, symbols, patent marks or other mould information. Some marks are associated with manufacturers or brickworks; others may identify a product, mould or production system. A mark should be researched alongside dimensions, colour, texture and manufacturing characteristics rather than treated as an isolated answer.

Frog shape matters

Record whether the frog is rectangular, rounded, deep, shallow, broad or narrow. Note whether the sides are sharply defined and whether the brick has one frog or another arrangement of recesses or perforations. The orientation of lettering can also be useful. If you can safely remove a loose brick, photograph both faces and all four sides.

Common identification mistakes

• Reading a partial stamp without photographing the full frog.
• Assuming a word automatically proves the manufacturer.
• Ignoring the brick dimensions.
• Confusing mortar, staining or damage with a mould feature.
• Assuming every brick from the same wall was produced at exactly the same time.

Frogs in older brickwork

Older and reclaimed bricks deserve particular care. A frog may contain dirt, lime residue, paint or weathering that hides its original shape. Cleaning can also expose a surface that looks very different from neighbouring bricks. Do not aggressively clean a historic brick simply to make a photograph clearer; preserve evidence where possible.

Use the clue with Find My Brick

Use Find My Brick with a clear face photograph and add the frog or maker's mark as a separate image. The result should be treated as a shortlist that still needs physical verification.