We give the following as copied at the Patent Office in London. Many of our Daguerreotypists have enquired of us in relation to the patents on the Daguerreotype in England.
To Autoine Jean Claudet, of High Holborn, in the county of Middlesex, glass merchant, for an invention of improvements in the process and means of obtaining the representation of objects of nature and art,--being a communication. [Sealed 21st November, 1843.]
These improvements consist in rendering the Daguerreotype picture susceptible of producing, by printing, a great number of proofs or copies; thereby transforming it into a complete engraved plate.
The process is established on the following facts, which have come to the knowledge of the inventor:--
1st. A mixed acid, composed of water, nitric acid, nitrate of potassa, and common salt, in certain proportions, being poured upon a Daguerreotype picture, attacks the pure silver, forming a chloride of that metal, and does not effect the white parts, which are produced by the mercury; but this action does not continue long. Then, by a treatment with ammonia (ammonia containing already chloride of silver in solution, is preferable for this operation), the chloride of silver is dissolved, and washed off, and the metal being again in its naked state, or cleansed from the chloride, it can be attacked afresh by the same acid. This acid acts better warm than cold.
2d. As all metallic surfaces are soon covered (when exposed to the atmosphere) with greasy or resinous matters, it is necessary, in order that the action of the acid upon the pure silver should have its full effect, for the surface to be perfectly purified; this is effected by the employment of alcohol and caustic potash.
3d. When a Daguerreotype picture is submitted to the effects of a boiling concentrated solution of caustic potash, before being attacked by the acid, the state of its surface is so modified that the acid spares or leaves, in the part which it attacks, a great number of prints, which form the grain of the engraving.
4th. When the effects of the acid are not sufficient, or, in other words, it is not bitten deep enough, the effect is increased by the following process:--Ink the plate as copper-plate printers do, but with a siccative ink; when the ink is sufficiently dry, polish the white parts of the plate, and gild it by the electrotype process; then wash it with warm caustic potash, and bite it in with an acid, which will not attack the gold, but only the metal in those parts which having been protected by the ink, have not received the coating of gold. By these means the engraving is completed, as by the acid alone it is not generally bitten in deep enough.