Answer: First of all, prop the gourds up off the ground so they are not in contact with the soil, and if possible, leave them on the vine until fully mature and the vine dies back. That way they will develop the most fibrous innards for the best sponges. When mature, the skin changes from green to yellowish brown, and if you cut one open as a test, you'll find plump, fully developed seeds inside.
Next, cure them in a warm dry place with good air circulation, checking them periodically for mold or rot. This process takes several months and must not be rushed. When cured and fully dry, the skin will be dark brown and the seeds will rattle freely inside.
Then, soak each gourd in tepid water to soften the skin enough that you can carefully peel it. After peeling, cut it into sections the size of the sponges you want. Clean out the seeds and any pulp from each section.
Finally, wash the "sponge" in a solution of one part household bleach to ten parts water. This will clean it and bleach it white. Good luck with your project!
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