Lead and pewter can be quite similar in appearance. And they have some similar characteristics. Each can be made shiny, but they quickly take on a dull blue-gray color. The primary difference is that lead is a basic element expressed as "Pb" in the periodic table. Pewter is a metal alloy that contains lead.
Lead
Hallmark traits of lead are its malleability, heaviness, resistance to corrosion and toxicity. Few metals can be bent with the bare hand, but lead can be. Lead is a relatively inexpensive metal. It has many specific uses because of its unique properties. It is often used in corrosive environments such or containers or barriers for highly corrosive substances.
Pewter
Pewter is a metal alloy; it is composed of multiple types of metals. Tin is the primary ingredient in pewter, which is much lighter than lead. Tin is also a very soft metal, but not nearly as malleable as lead.
Additives
Pewter's additives can include antimony, copper, bismuth and lead. Tin makes up about 90 percent of pewter and a combination of additives makes up the other 10 percent. The primary purposes of the additives are to increase the hardness and melting point of tin.
Obsolescence in Pewter
Because of lead's toxicity, it is very rarely used as a pewter additive anymore. It used to be the primary hardener. Though it's very soft, the tin/lead alloy was harder than pure tin. Lead was replaced by antimony because it was shown that lead-containing pewters could cause neurological damage in people exposed for long periods.
Summary
There are a few similarities in the two substances. And they're often mentioned together because of leads' historical use in pewter. But, they are very different substances. Lead is a pure element; pewter is an alloy. Lead is heavy; pewter is light. Tin and pewter are expensive; lead is inexpensive. They no longer have much relationship at all.