The International Herald Tribune recently ran an interesting piece about the potential impact of the AAMD's decision to depart from its "rolling 10 year provenance rule" for acquisitions in favor of one based on a 1970 date favored by the archaeological community.
I'm not sure I fully agree that all items without a pre-1970 provenance will become increasingly unsalable while ones with such a provenance will become increasingly valuable, at least across the board. What I do see is that this trend may very well impact the upper end of the market. It’s one thing to have doubts about something worth $250 and quite another to have doubts about something worth $2.5 million.
I suspect unprovenanced antiquities will still be collected, but a two-tier market may develop. Large auction houses like Sotheby's and Christie's will probably become less likely to deal in such materials, but they will continue to be sold openly in other outlets (unless it becomes illegal to do so).
I also suspect that ultimately this requirement may encourage further "repatriations by sale." It is no secret that the dollar's decline against other international currencies, coupled with increases in wealth in what have been traditionally viewed as "source countries," has already contributed to antiquities being repatriated to countries like Cyprus, Greece, Italy, Turkey and China. In addition, I'm certainly not aware that wealthy collectors or "private museums" in such countries are under similar constraints to only collect "provenanced material." Instead, at least in countries like Cyprus, Greece and Turkey, it is my understanding that once an artifact is repatriated, it must be registered with the state and then cannot typically be re-exported, at least legally.
I would be most interested in any outside comments on this topic.