Don't clean the coinsLet the people you are giving them to make that decisionAs you can tell from the answers here, collectors never want coins that are cleaned.
How To Clean Aluminum Coins
I am going to disagree with the ceramics engineer on several pointsMy orientation is from the glass end but I know a bit about ceramicsCeramics involves aluminum and silicon oxide materials and that is the major difference from glass which is silicon oxides with other alkali (sodium, potassium, and calcium) oxidesCeramics are not crystalline, they are bound together by vitrified materials, true, but that means glass like - the more glass, the more glass like - porcelain being the high end and requiring the highest temperaturesParts of ceramics never melt which makes them opaque and gives them their inner structure and texture and the ability to hold their shape while being fired Glass goes more or less molten while it is being worked and the processes involve keeping this stuff from sagging and distortingThe torch worker builds on a solid base and/or keeps much of the work cool to support the rest that is being heated in a torch flameThe furnace worker constantly rotates the work and adds more glass finally allowing the inner part to be stiffer while reheating the outside for shaping Glass is also shaped by putting a molten gob in a mold and pushing down (pressed glass) or blowing out (mold blown) to fill the mold Most heavy glassware glasses, bowls, plates, etcare pressed glass while most thin glasses and all bottles are blown Most ceramic ware including toilets are slip cast (liquid clay is poured in a plaster mold which sucks the moisture out of a layer so it stays in place when the extra clay slip is poured off) or it is pressed into molds The major difference between ceramics and glass is that at the art level it is possible to walk away from a ceramics piece and come back to it while glass must be constantly attended until stored in an annealer or it will sag or chill and shatter.
I wouldn't try cleaning themeven if you don't care about the value, they could be over time; and since they are gifts, they might be appreciated and keptYou could use a bit of lemon juice with an old toothbrush, gently rubbing it around on them Best wishes.
