I droped a small lamp in a piano and the corner got chipped. I need to fill the hole and give it the same black satin look. How can I make this repair?
This sort of repair is doable, but fair warning, getting a truly seamless repair is challenging to extremely difficult (read: nearly impossible without experience).
the same black satin look.
First thing re. the surface finish, in the photos the piano looks not satin but gloss, which is what one would expect on a piano.
Satin more normally refers to a definite step down from gloss (semi-gloss is essentially a synonym). If the surface gloss here is not quite as shiny as the paint on a new black car then it's likely it is just from some surface wear, but originally it would have been a full-on "wet look" gloss.
In any case, whatever the gloss level of the piano in the flesh it can be matched with the patch.
How can I make this repair?
There are multiple approaches you could take here any of which could give a good-looking repair if done well.
The first general approach, common in woodworking today, is to fill the void and then overcoat with a gloss finish, which is then flattened off or blended in and buffed/polished if needed.
The other main method and the one I would recommend is to use a black filler material that can be polished to a high gloss so that you do the whole job just with a single material.
There are multiple fillers you would use here that could work but how perfect the repair will be is hard to say. Here's a short list:
- black shellac repair sticks (sometimes called stopping)
- tinted/coloured liquid shellac
- tinted/coloured epoxy
If you can get black shellac repair sticks in the right colour that's probably the ideal thing to go with, but they tend to be available only from specialist suppliers and can be expensive for a one-off repair like this because you need so little. So for this reason and others I would suggest your best bet is to use coloured epoxy.
Type of epoxy
The epoxy doesn't have to be an expensive 'liquid epoxy system' as most pros use. As it is being coloured jet black here any slight yellow tone (as common to most cheaper epoxies) will be completely swamped by the black so there's no need to using a colourless or water-clear epoxy.
In practice this also means you can use a much cheaper epoxy, e.g. any epoxy glue from the hardware store with the appropriate setting time. And this will likely be in a smaller package size (still more than you'll need here) so you're saving in two ways.
I would suggest you go with an epoxy adhesive with a longer setting time to give you a little elbow room, although this could be done with 5-min epoxy (particularly in a colder environment where setting time will be longer than indicated on the packaging). But be aware that you must use the epoxy while it is still liquid for best results, it won't bond to the surface properly once it has started to set and it is far easier to inadvertently trap air bubbles manipulating it when it has become stringy or somewhat pasty.
Colouring the epoxy
The epoxy can be coloured with many black substances and yield an acceptable result. Two of the best options are black oil paint (artist paint) or dry black pigment.
With black paint you just need a dab or two to colour about a level teaspoon of epoxy deeply black, and it is important not to add too much paint to epoxy as it will weaken it.
With black pigment you can add quite a bit more if desired, but it is likely that just a small amount is all you'll need to get the mixture as black as needed. For this repair I'd estimate you'll need less than a pea of black pigment. Note: dry pigment is generally a very light powder and black pigment can be a very very light powder (the most common type is pure carbon) so it can easily become airborne if disturbed and will then settle on every nearby surface.... so be careful not to jostle it, don't sneeze on it and don't work in a draughty area!
If you happen to have access to an old photocopier or laser printer black toner can be used as your pigment.
To mix the epoxy for use here it's best to mix it thoroughly by itself first, then blend it with the colouring agent. You can do it all in a single operation but it's easier to ensure a thorough blend of part A and part B (the resin and hardener) if they are mixed before colouring.
Then you want to over-fill the divot. Don't attempt to fill it perfectly level with the surrounding surfaces, it's likely impossible to do anyway but it's always preferable to overfill and then remove excess and flatten off. You will probably need to make a small tent of tape (duct tape is probably ideal but masking tape will work fine) on the vertical surface to contain the epoxy and prevent it just dripping to the floor.
Much of the excess can be scraped away with a single-edged razor. Go slowly and carefully as you don't want to dig into the surrounding finish (tip: it can be advisable to scrape the corners off the razorblade against the unglazed rim of a plate or mug to round them slightly).
You can also remove all the excess and then smooth off just using various grits of abrasive paper, backed with something e.g. a cork block or a small offcut of wood. Because you want to damage surroundings as little as possible I would be very careful about using a truly coarse paper such as 80 grit to begin with, it'll take longer but starting with 100 or 120 grit would be safer. Then you progress to 180, then 220 grit, then 320, then 400.
After final sanding (approximately to 600 grit) with set-or-dry paper you can go over the patch and the immediate vicinity with very fine steel wool to create an even scratch pattern (use 0000 grade), or if you prefer you can sand further with even finer wet-or-dry papers, up to approximately 1200 grit.
Then you actually polish out the surface. In theory you can just buff the area briskly with a cloth, this can raise quite a decent gloss in some cases. You can try this and see how you get on as there's no downside, but in general to get a proper gloss you need to use a polishing agent.
If you have nothing suitable already the best sort of thing to use is probably an automotive finish polish. These are used e.g. by applying a little to a just-damp cloth, rubbing with a circular motion and then letting the residue dry to a haze before buffing off with a dry cloth, but follow the manufacturer guidelines for the product you buy. This may call for a powered polishing mop.
Best of luck!