My O' level chemistry days suggest that that might be lead chromate ... what ever it is its a fascinating result.
richard
Dave Carrington: Correct, Mr. T! Chrome yellow( Lead Chromate) is a pigment used to colour paint. O level chemistry I failed largely due to the fact that me & a mate were banned from the lab for being a little too adventurous when it came to the practical work: something to do with sodium chlorate & sugar, as I recall...