## Facts

- Patentees obtained a U.S. patent (July 29, 1841) claiming an improvement in making door and similar knobs from clay or porcelain.
- The knob design used a metal shank/spindle secured by a dovetail-shaped cavity in the knob into which molten metal was poured to form a screw and fasten the shank.
- The accused infringers manufactured and sold similar knobs, leading the patentees to sue for infringement in federal circuit court.
- Evidence showed that doorknobs, metal shanks/spindles, dovetail cavities, and the fastening method using metal were already known, including for knobs made of wood or metal.
- The asserted novelty was primarily the substitution of clay/porcelain for wood/metal in an otherwise known knob structure and fastening method.
- The trial court instructed the jury that if the fastening method was already in use with metal, wood, or other materials, the patent was invalid; the jury returned a verdict for defendants.
- After denial of a new trial, the patentees sought review by writ of error.

## Issues

1. Whether a patent is valid when the only claimed difference from prior devices is substituting a known material (clay/porcelain) for another (wood/metal) while using an otherwise known structure and fastening method.
2. Whether the claimed improvement required inventive ingenuity, as opposed to ordinary mechanical skill, to satisfy the patent law requirement of invention.

## Decision

- The Supreme Court affirmed the judgment for defendants.
- The Court held the patent invalid because the change amounted to using a different known material in a known device and did not require more ingenuity and skill than that possessed by an ordinary mechanic acquainted with the business.
- The Court approved the trial court’s instruction, treating the “invention versus ordinary mechanical skill” determination as a question properly submitted to the jury on the evidence.

## Legal Principles

- A patentable invention requires more than the work of a skilled mechanic; it must reflect a level of ingenuity beyond ordinary mechanical skill in the relevant art.
- Substituting one known material for another in an existing device, where the structure and mode of operation remain the same, is not patentable absent additional inventive contribution.
- Practical advantages such as a better or cheaper product do not, by themselves, establish patentability when the claimed advance is an obvious material substitution.

## Conclusion

The Court invalidated the doorknob patent because it claimed only an obvious substitution of clay or porcelain for wood or metal in a known knob structure and fastening method, and thus lacked the inventive ingenuity required for patent protection.


Hotchkiss v. Greenwood, 52 U.S. (11 How.) 248 (1851)