To keep your arrangement of 12 white roses and 12 purple roses in a glass vase looking fresh and beautiful, follow these flower care tips:

1. **Fresh Water**: Change the water in the vase every 2 days to prevent bacterial growth and keep the flowers hydrated.

2. **Trim Stems**: Trim the stems at a diagonal angle before placing them in the vase to enhance water absorption and prolong the flowers' lifespan.

3. **Remove Foliage**: Remove any foliage that will be submerged in water to prevent decay and maintain water clarity.

4. **Avoid Direct Sunlight**: Place the vase in a cool, shaded area away from direct sunlight and drafts to prevent wilting and premature aging of the flowers.

5. **Monitor Blooms**: Regularly check the arrangement for any wilted or faded blooms and remove them promptly to maintain the overall appearance of the bouquet.

By following these care tips, you can ensure that your arrangement of white and purple roses remains fresh and vibrant for as long as possible.