I don't know what kind of door your talking about, or what finish is on it now, but a good way to darken a finish a bit is to use an aerosol toner.
Others may have different methods.

Hi,

Thanks for responding. The door is a maple veneer and originally had a dark stain (jacobean i think) and a poly finish. It was sanded, wiped and a coat of ebony stain put on it. Still not as dark as I would like though.

ella

Stains are usually meant to go on bare wood, not already finished wood. The exception to this is a gel stain that when used this way becomes a glaze. There is a limit, though in how much darker you can go before the finish starts to look muddy and opaque. Glazing technique More

Here is a link that might be useful: Glazing

Hi bobsmyuncle,

Thank you so much for the link - very helpful indeed! I do believe that's what the builders will do ie glaze. They will then give it 3 coats of tung oil, as i understand it.

Appreciate your help,
ella

There is "true" tung oil, and there are 10 times as many things called "tung oil finish" that are not tung oil and do not contain any tung oil. Depending on the brand, they are either thinned varnish, AKA wiping varnish, or a (linseed) oil-varnish blend. Neither of these types are bad products, it's just not what you think they are if you read the label. Real tung oil is relatively expensive, hard to use successfully, and not appropriate for over-coating another finish.

Here is a link that might be useful: Oil finishes and other misleading labels.

The OP still hasn't established whether this is an interior or exterior door. I think that will have a bearing on the type of stain and finish.

Consering tung oil, I have restored finishes on antiques where I have removed the finish but retained the patina followed by several hand rubbed coats of tung oils. It produces a very firm durable finish. BTW, I use Old Masters brand tung oil.