Several months after the publication of the tablet and after several scholars had declared the text a fake, the State of Israel put the owner, Oded Golan, and other individuals on trial in Jerusalem district court, for this fraud and for other infractions. After seven and a half years of periodically hearing testimony from 130 witnesses, in March 2012, the judge delivered a 500-page opinion explaining the complexity of the case, in which experts contradicted experts. The judge did not find the Jehoash inscription to be authentic but felt there was enough doubt to acquit the defendant of the major criminal charges. In October 2013 the court ordered the Israel Antiquities Authority to return the tablet to its owner. The tablet was returned the following May.Geologists seem to be divided on whether the Jehoash (Joash) inscription could have been faked. Most philologists (myself included) think it is a forgery, but at least one has declined to declare it so, although even he makes no positive case for it being genuine. As usual, if a Semitic philologist ever wishes to publish a peer-review article making such a case, I will have a look at it. Meanwhile, I agree with Ed Greenstein. It's a fake.
The judge, overwhelmed by the diverse testimony, was inconclusive. However, the judgment of scholars who read ancient texts and analyze their language and writing is clear: no textbook of ancient Hebrew inscriptions will ever include the so-called Jehoash text; no historian of ancient Israel will ever count the inscription as a source; no grammarian or lexicographer of ancient Hebrew will ever include words, phrases, or forms found in the inscription as genuine data.
Background on the inscription is here and here and many links.