How do I clean thick alkali residue off of windows?
Try white vinegar
Try Bon Ami spray. It is very effective at removing buildup. You can find it at Home Depot.
Good idea from Maysel, an acid + a base makes a salt, or removes the alkali. Rinse well with water. Hopefully the windows are not etched from the alkali.
I use a 50/50 mix of white vinegar and water plus a few drops of dishwashing detergent in a spray bottle. Spray it on, let it sit to do it's work, then clean it off. Repeat if necessary. Wishing you the best.
I used trisodium phosphate (TSP) mixes with water or you can get it at the hardware store in a spray bottle and just have a pail of water to rinse the rag in.