U.S. law forbids the sale of relics from the Titanic, and allows only for salvaged items to be put on public display, not on the black market.
Yet, experts say that dozens of expeditions to the Titanic have plundered the ship, and taken their toll on the liner.
Tom Utley, whose marine engineering firm makes windows and port lights for many ships, tells ABC News that he was sent a stolen Titanic porthole to inspect.
Utley says it's worth $36,000.
"It took three of us to lift it, and it was an ugly-looking thing," he said. "Nobody would have kept this for aesthetic purposes, and above ground it probably would have corroded, whereas on the Titanic it would have been perfectly preserved 2½ miles down."
ABCNEWS.com asked him how much the porthole would have been worth at the time the Titanic sunk.
"About half a crown," he said.
Half-crown was a denomination of British money worth two shillings and sixpence, or one-eighth of a pound.
Calculations show that the porthole is worth $36,000 on the black market today; it was worth 22 cents attached to the wall of a sinking state room in April 1912.
Expeditions using minisubmarines, some of which have landed on the deck, have caused extensive damage.
Bill Willard, a Titanic expert who says he has been down to the weckage twice with a midget submersible, tells ABC News that the liner was being badly damaged by the expeditions, some of which now carry tourists.
Concerning one reported "rogue" expedition, Willard said to ABC News, "It did do some damage at the site, and they tried to break into the cargo hold to recover things."
