For the past few years now I've been selling small paintings on my website and shipping them out myself and I've had to figure out the best way to pack them safely so they don't arrive damaged in any way. I use the USPS free flat rate boxes - usually the Medium size - as these allow for extra room around the painting for padding, in case the box gets stepped on or dropped the painting won't be touched.
Before shipping the painting out, I inspect it once more to make sure everything looks good with it. Then I dust it off if needed and seal it in a clear bag to keep dust out and protect it from anything else like liquids and so on.
I then go through my packing materials that I've acquired over the years from ordering products online. Usually when I order something on Amazon, inside the box will be some airbags or some kind of packing material and most of the time I will save it for reusing in the future.
I place air bags in the bottom of the box about halfway up and then place the painting on top of those. I also cover the painting in packing paper, just for added security and I will also cover it with a bit of bubble wrap as well for more padding. I keep the painting in the center of the box away from the edges to keep it safe from being damaged.
Then I fill the rest of the box up with more airbags and newspaper to keep the painting from moving around. At this stage to test my packing, I will hold the box closed and shake it in all directions to see if I can hear any movement. I usually never hear anything moving around and that's a good sign. Now it's almost ready to be shipped out!
The last step is taping the box up and getting a shipping label on it. In the past I've gone to the post office, waited in line, and got the label put on there at the counter after paying, but now I print the label myself and pay for it through Etsy. Now I attach the label and tape up the box and it's ready to be shipped out.
Check out my shop to see Available Paintings for purchase.