It looks like I may have deposited less than the minimum amount, which seems to be 0.001 BTC (though who can blame me).
ChipMixer works in multiples of 0.001 BTC. Anything you deposit will be rounded down to the nearest 0.001 BTC increment, with whatever is left over treated as a donation/fee, since you don't actually pay any fees on the mixing or withdrawal process. If you deposit <0.001 BTC, it will all be treated as a donation. If you were to deposit 0.00543 BTC, for example, you would be credited with 0.005 BTC, and 0.00043 BTC would be given as a donation.
The smallest chip you can withdraw is 0.001 BTC. Chips then go up in size in powers of 2, so 0.002 BTC, 0.004 BTC, 0.008 BTC, and so on, up to 8.192 BTC.
This is all explained on their FAQ page. It works normally for me via the Tor link I posted above.
Thanks for explaining that so succinctly.
I take it there are no differences in terms of security when using large or small amounts, including 0.001 BTC?