I've searched and searched but I cannot find anything on the internet that looks close to my bad stain job, so here's the low down: I'm finishing my dining room tabletop and chair seats. I'm using oil based wood stain in dark walnut. I've sanded them all down. I don't know the wood type because I bought the table second hand. I've attempted two chair seats and they both have turned out like the picture I've attached...what am I doing wrong? Do I need wood conditioner? Should I use gel stain instead? I'm so lost! Any help is much appreciated. :) here is the after staining: Here is the before:
what am I doing wrong?
This looks like a classic case of not preparing the wood fully for new stain. When you don't remove the previous finish and expose bare wood uniformly it won't look even, even sometimes if not staining a new colour and just applying new varnish.
When you're sanding off old finish and you think you're done there's an easy way to check, you just need to dampen the wood (usually done with water, mineral spirits or denatured alcohol). If you haven't gotten down to bare wood it'll show up immediately, where the bare areas will go darker than the areas where some finish remains in the surface wood fibres.
This test can be repeated as often as necessary to check progress, but, you should let the wood dry before commencing sanding again.
In addition to not sanding enough I can see at least one area where there are cross-grain scratches, which make the wood stain more darkly. If you need to sand to prepare wood it's very important usually to finish sanding in the direction of the grain, until all cross-grain scratches are gone. This often takes much, much longer than you want it to (most people starting out get bored and give up, we've all been there!) but it's a necessary part of the operation.
You can sand purely orbitally if you do it conscientiously and go to a fine enough grit (possibly above 240) and especially if you use a random-orbit sander, which is far better for finish sanding than a basic orbital sander. But it's still best practice to finish sand, by hand using a block to back the sandpaper, going in the direction of the grain.
Do I need wood conditioner?
Probably no, but sorry but we can't tell yet. You'd need to get back to bare wood, test for whether it stains evenly and then "condition" the wood if you find it's one of the (few) species that requires it.
Pretty much the one and only job of "wood conditioner" is to help reduce the tendency of wood stain to be absorbed unevenly, leading to the dreaded blotching. I use quotes here because it's a stupid name for a product that isn't needed since they're just very dilute finish, which anyone could make for themselves for a fraction of the price of the commercial versions (which are mostly solvent!) o_O
Should I use gel stain instead?
Just to let you know to begin with "gel stain" is a coloured varnish with a gel consistency. It's not a stain in the normal sense of the word despite the name. Yes, another dumb name for a product, but at least in this case a useful product :-)
Anyway, gel stain can actually be a very good choice for this sort of thing because it's not stain. So it doesn't get absorbed by the wood, effectively hiding whether the wood is irregularly absorbent (this is why gel stain is a good pick for pine, which is infamous for absorbing stain very unevenly).
What to do now
I really hate to say this (I hate sanding more than most) but you have much more sanding ahead of you, unless you want to switch to scraping — see here for why it's so much better.
You must now remove the wood that has remaining finish on it as well as the wood that has now absorbed the oil stain.
If this hasn't put you off doing this sort of project again for future reference sanding is often the worst way to remove previous finish. It's much better to rely on a chemical stripper which are of course designed for doing this exact job.
Using stripper doesn't make finish removal a walk in the park by any means because there's still a lot of tedious scraping and wiping to complete the removal of the finish, but it's better in a few key ways and it saves turning the old finish (and any crud on top of it) into fine dust that gets everywhere and is potentially harmful to you, pets etc.