Making your own copper sulfate solution of 1 mg contained copper per drop is very easy. Just measure out the blue copper sulfate crystals and the water.
This is about 5/8ths of a teaspoon, or 5 of the 1/8th teaspoons, or about 4.7 grams or 4700 mg of 99% pure copper sulfate pentahydrate (containing 25% copper by weight), or 1175 mg of contained copper being put into a 2 oz. bottle, containing about 591 drops per oz. or roughly 1182 drops, making roughly a 1 mg per drop solution.
4700 mg x 25% = 1175 mg
Further sources and information:
https://butternutrition.com/vitamin-d-supplement-warning/
https://www.amazon.com/Copper-Sulfate-Crystals-10lb-FINE-Crystals/dp/B018YIMJ3U/
Actual ratio: 1 teaspoon copper sulfate crystals to 5 oz. of water.
There is a way to purify copper sulfate. https://www.robolab.in/purification-of-copper-sulphate-by-crystallization/
It appears you make a crystal, strain the solution as you go, then crush it afterwards.
Just made mine. Thank you for sharing this Jason.