Re: bichromate gum
Thanks to Sam, Christina and Judy for the helpful replies. Speaking of chemical purity, my dichromate isn't exactly reagent grade - it is sold as "sodium potassium dichromate" by the kilogram for use as a pottery glaze. That seems to be the only way to buy it in New Zealand now. I recently acquired some photo chemicals from an old hoarder which included a 1oz bottle of pot dichromate with a pharmacist's logo on the label and a price dating back to before we converted to decimal currency (1967) - the contents had formed a single crystal Obviously in those days you could buy stuff like that over the counter, but now we have an international bureaucratic network dedicated to eliminating such hazards now (also removing Portriga Rapid paper and mercury lightmeter batteries, and replacing inert aerosol propellants with explosive ones). One of the advantages that I thought the "bichromate first" technique might offer is the opportunity to take a more painterly approach to the colouring step - e.g. use more colours, follow the image a bit, and leave some blanks. Does that make sense? Don Sweet
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