Lead is also used in ceramic glazes and as a stabilizer in plastics. Lead was used extensively as a corrosion inhibitor and pigment in paints but concerns over its toxicity led to the CPSC in 1977 to ban the use of lead in paint for residential and public buildings.
The first digit assigned to all Visa cards is four, and the second through sixth numbers are connected to the financial institution. Then, either the seventh through 12th numbers, or the seventh through 15th, are the account number, while that final 13th or 16th digit is the check number.
I'm not sure if you're asking what the card number is on a Visa debit card, or if it is different than a Visa credit card... so I will try to answer both. A Visa card # is a 16-digit number, that uses a specific format. In order to be a valid number, the 16 digits have to work within the Mod 10 algorithm. All Visa numbers start with a 4. MasterCard numbers start with a 5, Amex is 3, and then there are a few others, including Discover card, etc.