Stainer

It appears there may be a typo in your request, as there is no recognized musical instrument or standard term known as a “miniature playing brass stainer.” It is highly likely you are referring to a miniature brass instrument, which is often crafted as a decorative collectible or a novelty scale model of standard brass instruments like the trumpet, trombone, or French horn. While these items are intricately detailed—often featuring working valves or slides—they are typically non-functional or purely ornamental, meant for display rather than professional musical performance. If you were instead referring to a specific historical tool, a specialized staining technique for brass, or a different object entirely, please provide a bit more context so I can better assist you.