Numismatic Part: Slabs on occasion have something on them that it would be nice to remove. Generally it's some adhesive from a label. Past experience has shown me that isopropyl alcohol is often good for that job. I use the 70% stuff that is also labeled "rubbing alcohol". BUT A WARNING I also know that the 90% stuff will "melt" the plastic. And at the moment I have some. Non-Numismatic Part: So here's a question for the chemists among you. How much distilled water do I have add per unit volume to dilute 90% to 70%?
I don’t mean to sidetrack your question. Yes, alcohol absolutely can damage plastic. A three dollar bottle of Turtle Wax lens cleaner will do the job with the added bonus of polishing out scratches from the slab. I believe the bottle I purchased three years ago will last my entire numismatic lifetime. It gets the gooey sticker stuff off with a simple wipe.
I don't believe there are any rules that say that you can't pass your collection to your family along with the leftover Turtle Wax lens cleaner. Great tip though Randy. I saw that once before and forgot about it.
I use the Novus polishing trio to remove scratches. But they are no good for sticky residues. Thanks for the Turtle Wax lens cleaner suggestion.
A little WD-40 will remove any adhesive and not hurt the plastic. Or 3-in-1 oil, but then you have to get the oil off.
OK. Here’s the solution … pun, pun, pun. V70 is the volume of 70% you want, and V90 is the amount of 90% needed to make V70. The mass of isopropanol is the same in either case. So: V70 x 70 = V90 x 90. Solving for V90: V90 = 0.778 x V70. If you have a certain amount of V90 and want to use it all to make V70, then the equation is: V70 = 1.29 x V90. Ideally, V90 should be put in a graduated cylinder and brought up to V70 with water. But it will be close enough to put V90 in a container and add a volume of water equal to V70-V90. The two methods are not completely identical because of partial specific volume, which I won’t go into. Say you want 1000 ml of 70%. Put 778 ml of V90 in a container and add 222 ml of water. Say you have 500 ml of 90% and want to use it all to make 70%. The V70 volume is 1.29 x 500 = 645 ml. Put the 500 ml of V90 in a container and add 145 ml of water. Cheap plastic graduated cylinders can be bought on eBay or from Amazon. The plastic in these cylinders (polypropylene) is not affected by isopropanol. Cal
I have successfully removed adhesive sticker residue with GooGone with no adverse effects. The GooGone will leave a bit of oily residue so I wipe that off thoroughly. I also use the Novus polishing pastes for cleaning up scratched slabs.
@calcol So as I read it I should increase the volume by 30%. The volume on the container is listed as 10 FL OZ (296 mL). So adding 3 FL OZ (90 ml) of distilled water should be close enough to being correct.
Yup. 296 ml of 90% x 1.29 = 382 ml 70%. 382 -296 = 86 ml of water to add. 90 ml is close 'nuf. But the way I remove labels from slabs and just about anything else: I buy little packets of adhesive tape remover at the drug store or Amazon. The packets have a little square of gauze soaked with remover. Works great, and because it's designed for skin, safe and non-irritating. I even carry a few in my go-to-coin-show-bag. Cal
