This is an inexpensive and easy project that can be completed in a total of under 30 minutes. You'll need:

Small plastic container
There are a variety of sizes for storing small beads, etc. Six for $4 on Amazon and many hobby stores.

5 minute Epoxy
5 minute is perfect - nothing faster.

Gold, copper or bronze paint (or a combination of two.)

Print of gauge face/s
I hunted images on the web and made a sheet. Laser or run-proof inkjet. Card stock or photo paper.

Step 1: Select and Cut a Gauge Face

I have a variety of little and not so little plastic containers, so printed gauge faces for them all. Just search the web for them - "antique pressure gauge" "old pressure gauge" and so on. I put together a sheet in Photoshop - any graphics program will work.

You want a print that won't streak or run when it gets wet - so laser or permanent ink-jet.

Rough cut a gauge face, then place your plastic container on top of it - bottom on the image. Depending on the gauge, you may see that the gauge face itself acts as a guide - or you may need a guide - grab a marker and trace around the plastic if needed. Remember to cut it a bit smaller.

Drop the paper in the plastic container to check for fit - again, a bit small is OK. Don't force it in just now - you'll have a problem removing it. You can use a dental pick or piece of tape. The paper should drop in all the way and not need to be forced.

Step 2: Cut the Plastic and Clean It Up.

Next, cut off the un-needed plastic. Do you want a deep faced gauge or shallow? This is personal preference. The actual cutting can be with a file or Dremel tool. Dremel is the easiest. Cut the plastic or file through it - be careful here - you can break or shatter it. A crack or two is OK - you won't see them.

Next, trim off the excess/melted plastic that forms when cutting - especially with a Dremel. Any knife will work. You're not looking for a glass-smooth finish.

Step 3: Contour the "gauge"

Do you want a flat backed or contoured back gauge? A contour makes the gauge looks like it's sunk into a curved or contoured surface - looks cool on curved surfaces.

1: Sand the rough cut base smooth - required for a flat back, optional for contoured but makes the next steps easier. Use very fine sandpaper and go slow to avoid melting.
2: Flat back? Skip to next step. Contoured - continue on with this step.
3: In this case, I'll be using a piece of PVC as the fake steam tank. So I take the PVC, wrap 200 grit sandpaper around it, and sand - push the plastic back and forth, lengthwise. SLOWLY - or you may crack the plastic. After a couple of dozen passes you'll see the plastic is contoured to the tube. For a final step, use very fine sandpaper and do a few more passes.

You'll now have a perfectly contoured gauge base.

Step 4: Epoxy the Face Into the Plastic

First, do a final fit check. The paper should drop in and out. Mark the bottom of the face so you can see the orientation from the back.

Mix up some epoxy. You'll want enough to make it 1/8" deep. Place 1/2 the epoxy in the plastic. You'll probably have a lot of small bubbles in the epoxy - a blow dryer on high for around 15 seconds blowing on the epoxy will remove them - don't melt the plastic! Place the face in the epoxy, with the mark down. "Down" may differ on your project. Use something flat to make sure the gauge face is pressed down as far as possible. I use a cut Q-tip (no cotton.) Check the face for air bubbles and press/work any out.

Next, add the remaining epoxy to the back of the paper so the gauge face is totally covered.

Wait 30 minutes or more. The epoxy will be pretty well set, but your finger nail can still dimple it after 30 minutes. Next it's time to paint.

Step 5: Paint, Paint, Paint.

What paint to use? I prefer latex, but it will need a clear coat. You can also use nail polish or model paint. Latex is just so much easier.

Paint the inside - give it a couple of coats.

Paint the outside. Painting the inside and outside gives added color and depth. You can also paint just the inside for a different look.

Colors, texture, etc. is really personal preference. I like to put some bronze and copper and lightly mix them as I go - I "dab" the paint on - when it dries, this looks like the vintage two tone paint job you see on old equipment. You can also spray paint, but you'll have to mask the face. With latex it's easy to clean.

Many gauges have a different color lens ring - metal, black, etc. Again, personal preference. For a clean, different colored bezel you want to wait for the paint to dry fully then use masking tape for a clean edge - see the next step.

Step 6: Clear Coat and Mount!

To protect the paint from scratching, you'll want to use a clear-coat. Spray or brush. I use several coats. Clear nail polish works great. On some applications I'll sink the gauge face into my prop and cover with epoxy. It really depends on the project and look you want.

You can also add scratches, discoloration, patina, etc.

Mounting depends on the project. I typically use epoxy as it works on any surface. If you want, you can also put an LED behind the face for a backlight.

I usually make three or four gauge faces at a time so I have them for future projects. I'll do everything but paint them so I can match the paint to my project later on.