Worried about slipping on the bathroom floor, I purchased a 1 Litre bottle of "DTA Domestic Anti Slip" at Bunnings Hardware (about $40, made by DTA).
This is not a coating for the tiles, but an acid which etches the tile to make it rough (as used to etch glass). The bottle comes with numerous safety warnings. I found a broom, with plastic bristles and a long handle, an effective way to apply the acid (along with rubber gloves and eye protection). Realising that I would not walk right up against the walls, I left a strip about 5 cm wide untreated around the walls, to avoid splashing the liquid on the walls.
The bottle says it will treat up to 9 square metres, but I found there was about half a bottle left after finishing the bathroom, so I also treated the kitchen floor and half the balcony. In total the one litre treated about 14 square metres of tiles.
The treated tiles have a slightly satin finish, compared to the glossier untreated tiles. However, the effect is not readily apparent and quite pleasing. While etching the floor tiles, the treatment had no apparent effect on the chrome metal drains in the floor, paintwork, grout or wall tiles (it did not even kill the mould in the shower recess).
To test the surfaces, I washed the floor with suds from the washing machine, which usually leaves the tiles too slippery to walk on. The treated tiles were no longer slippery and were safe to walk on. Assuming the tiles are really etched, the treatment should be long lasting. However, I will need to see what happens when the floor gets dirty.
According to DTA the product contains Fluoride.
Slippery tiles may seem a trivial topic, but slips and falls cost about half a billion dollars per year in Australia in hospital treatment.