Can I use varnish instead of polyurethane sealant?

Polyurethane will soak into and adhere to the grout, but glazed tile is generally non-porous. The polyurethane may initially stick to the tile, but it will soon peel off.

You'll need to sand them down. A power sander will make the job much quicker.

You don't have to. It depends on what texture you want.

I don't think you should use a cast iron pan but it could work if you are desperate. I would definitely use a gas stove.

Tape will not last as long as glue, especially a glue made for paper. There's no reason you can't use origami paper, though.

Varnishing your painting is a good idea. The varnish will help protect your painting from dust, yellowing, and sun damage. It also adds a nice sheen that can help the...

Two coats of varnish are usually enough for an acrylic painting. Be sure to apply the varnish in thin coats, and wait for each coat to dry before applying another.

You'll create bubbles in the varnish that will harden onto the surface of your acrylic painting. With this in mind, it's never a good idea to shake your varnish.

Varnish dries a lot faster than acrylic paint. Because of this, you should never apply varnish to a painting that isn't fully dry.

Sanding is the main way to remove old varnish. If that doesn't work, there are paint removers and gels that you can apply, wait about 15 minutes, then scrape away....