I have a jewelry pieces with dark blue glass that doesn't glow very bright. Is it uranium gla

Actually, yes! There are some colors in jewelry that don't glow as brightly as others because the dark color subdues the glow. Sapphire blue is the most common, but this can also happen with dark green, citrine yellow, and topaz colors.

If you are unsure about a piece, you are welcome to send me an email with photos and I can have a look!