Casascius coins, also called Casascius physical Bitcoins, are physical metal coins that hold some units of Bitcoin. They were created by a Bitcoin user Casascius Mike Caldwell and who decided to transform virtual currency into physical coins. The coins contain an embedded piece of paper with digital Bitcoin value, wrapped by a tamper-resistant hologram. Casascius coins are available in 1, 10, 25, 100, and 1000 BTC increments.

The coins enable holders to perform physical transactions. The first person to uncover the private key of a coin gets the value embedded in the coin, and afterwards, the Bitcoin value is lost. It is impossible to read the private key on the coin without damaging or destroying the hologram, which reveals a honeycomb-like tamper-evidence pattern when peeled.

The piece of paper inside each Casascius coin has a private key that represents the Bitcoin value of the coin. Redeeming the private key back into digital Bitcoins is currently available with a patched reference client and many of the alternative clients.

How does a Casascius work?

Each Casascius coin holds the private key to the digital value of a particular bitcoin account. Even if the coins are designed to reveal the worth of an account, they’re actually just secure containers for the digital information that reveals the bitcoin’s value. The eight-character code on the outside of the coin corresponds to the first eight characters of an individual bitcoin address, which is assigned specifically to that coin.

The digital bitcoin the Casascius coin represents is located in a virtual wallet. The digital coin connected to each Casascius is accessible only to the person who has the private key from the physical coin.

To spend a Casascius, the owner uses the code embedded into it to access the digital bitcoin online. The private key code can be imported directly into bitcoin clients or exchanges like Armory, Blockchain.info, to deposit funds.

Where and how can Casascius coins be purchased?

Casascius coin can be purchased online, either with bitcoins or using other forms of payment. Bitcoins are the only accepted form of payment for Casascius coins on Caldwell’s website. However, other forms of payment can be used to purchase it from sites like eBay, BitMit, MemoryDealers, HardBTC.org (UK), Bittiraha.fi (Finland), microbitcoin.fr (France) and BitInnovate.com (Australia).