How thick should a stained glass window in a door be?

Question

I'm remodeling a bathroom in an American Foursquare house built in 1920, and we are trying to stay mostly true to the wonderful vintage feel of the house. The bathroom had been poorly remodeled in the 70s and it had what I would consider an ugly 1/8" "frosted" window that was 20" wide and 36" tall.

I removed the glass and stripped the lead paint that had been added to the inside portion of the door.

I haven't decided on a design yet, but I have been in contact with a stained glass window maker, who has been a tad pushy, so I haven't asked him this question (to reduce interactions). But they also recommended adding a solid pane of glass on one side of the window, but that would mean I cannot use a similar molding/trim to hold the glass in. I'm not sure why that would be necessary, as none of the other (exterior) stained glass windows in the house has that and they are original and in good shape - and this is an interior door.

Is there a way to measure the thickness of our existing stained glass windows and would that be a good reference for what the thickness should be for the glass in the door? One is oval and doesn't open. The other is side-hinged with a pretty thick frame:

But even if I could measure them for comparison, having stained glass in a door is very different from a window and I don't know how that affects the thickness requirement to be durable.

The main reason I'm asking is because I need to make the moldings/trim for around the window and I need to know how much of a gap to leave.

Incidentally, I also intend to add stained glass to the lower original window sash, but for not, I'd like to focus on the door.

This is the door, for reference. It is solid wood. The window is on the table behind it, but the photo is old and I've since finished stripping it.

Answer 1

You probably don't want to be copying the thickness of the original glass. It's debatable whether it would conform to modern safety standards.
You can get really good 'fake' stained glass these days [known as overlay stained or leaded glass], which is actually surface-mounted onto a sturdy tempered safety glass sheet. It doesn't suffer from droop, sag or bend over time like the real thing & stands up to reasonably close inspection.

This is the glass insert in my front door [sorry, needs cleaning] which you can see from the logo bottom left is actually toughened safety glass. The glass diamonds & 'not really lead but it's hard to tell' are simply stuck to the face. It's also the outdoor-facing pane of what is actually a sealed double-glazed unit, 29mm in this case but you can get them as narrow as 5mm. In this instance, the inside pane is the one with the slight privacy ripple to it. You can also get it as a single pane, treated similarly on both sides; in effect, the same pattern stuck to both sides of a single pane of toughened glass.

This particular pane has been facing the worst of the British weather for over 20 years & is still as good as new.

^{Click for full size}

The design doesn't have to be as simple as mine. You can get just about anything made, including copies of existing panes, if you wanted it to match.
Example - https://www.leadbitterglass.co.uk/stained-glass/

In the UK, the thinnest toughened glass allowable is 4mm, though for a large door panel, I'd be looking at 6mm.
You can get it in standard thicknesses, 4, 6, 8, 10, 12, 15 & 19mm, though the top end of that scale is for large store windows & eventually up to walkways, safety barriers etc.

Note also that the 'lead' ends at the frame edge, so if you've got 6mm glass, you need only a 6mm accommodation for it.