In Woodcraft and Camping, "Nessmuk" (George Washington Sears) described his bug dope" as follows:
It was published in Forest and Stream in the summer of 1880, and again in '83. It has been pretty widely quoted and adopted, and I have never known it to fail: Three ounces pine tar, two ounces castor oil, one ounce pennyroyal oil. Simmer all together over a slow fire, and bottle for use. You will hardly need more than a two-ounce vial full in a season. One ounce has lasted me six weeks in the woods. Rub it in thoroughly and liberally at first, and after you have established a good glaze, a little replenishing from day to day will be sufficient. And don't fool with soap and towels where insects are plenty. A good safe coat of this varnish grows better the longer it is kept on—and it is cleanly and wholesome. If you get your face and hands crocky or smutty about the camp-fire, wet the corner of your handkerchief and rub it off, not forgetting to apply the varnish at once, wherever you have cleaned it off. Last summer I carried a cake of soap and a towel in my knapsack through the North Woods for a seven weeks' tour, and never used either a single time. When I had established a good glaze on the skin, it was too valuable to be sacrificed for any weak whim connected with soap and water. When I struck a woodland hotel, I found soap and towels plenty enough. I found the mixture gave one's face the ruddy tanned look supposed to be indicative of health and hard muscle. A thorough ablution in the public wash basin reduced the color, but left the skin very soft and smooth; in fact, as a lotion for the skin it is excellent. It is a soothing and healing application for poisonous bites already received.
Nowadays, I'd avoid adding the pennyroyal oil, as it is known to be a liver toxin.
However, it may not be necessary to make up a solution, since pine tar by itself can do a pretty good job of repellent biting insects. Yesterday I gave Granpa's Pine Tar Soap as test as insect repellent, during the opening day of archery deer season here in Pennsylvania.
When I took my morning shower I used the pine tar soap as both shampoo and to wash my skin.
The temps ranged from the mid-60s up to the 80s in the afternoon. There were plenty of mosquitoes and gnats flying around but none of them would land on me, except for a single skeeter that landed on my pant leg, where I squashed her (only female mosquitoes bite).
It remains to be seen if the pine tar soap repels biting flies, but for mosquitoes and gnats it works. I may even wash the sniper veil I use to break up my outline in it, and maybe some clothes. You smell like a campfire after washing with pine tar soap, but that beats getting bitten.