Out on the internet, you can learn how to make a homemade incubator.

So my duck had eggs but my sister and i picked them up a while after thinking they weren't fertilized but when we cracked one open it has vanes???? anyway we don't own an incubator and we're trying to hatch them without one, we have a lamp and a thermometer so the heats all good! But we don't know how to make it more humid in there for them? How can i do that?