How can I erase files from a recordable CD?  

i'm not so sure on this but i'll try to help out

you need to make sure the disc is rewritable. not all CDs and DVDs can do that.
and the next thing to make sure is that you need to have a burner that can write AND re-write. again, not all CD/DVD burners can re-write.

a recordable CD could mean it can be written on. it could or could not be rewritable.

There are different CDs and if your CD is CD-R (which means rewritable) then you can't delete the files in there and it also depends on your CD drive if it supports CD rewriting. CD-RW (rewritable) is the one who supports to be deleted and then be written again with files.

recordable and re-recordable are two different types of CDs. with recordable, you can only write to the disc once. and once files are there, you can not use if again to recordable some more files or change the contents of it. with re-recordable or rewritable, you can do use it again and again, record, delete, change the contents. just like you are having a harddisk or a flask disc or floppy disc, etc.

The file format of a CD is different from that of a magnetic or solid state medium and individual files can't be erased. Only a re-writable (CD-RW) allows you to erase and write the CD again.

If the CD is CD-R (recordable) then you can't erase what has been written and you can only add data if there is space and if the CD hasn't been closed.

To be able to erase a CD in order to write new files you have to use a CD-RW type, which is more expensive than a CD-R.

For recordable CDs (CD-Rs) once they are recorded then they cannot be modified. Unless of course if you burn it using a multi sessions format, in which case you can add more data into the remaining space on the CD.

ReWritable CDs (CD-RWs)on the other hand can be written multiple times, so basically you can modify your data in the CD (erase, or add more data) just like you do in a hard drive or flash disk. However, the rewriting cycles is low (about 1000 times) compared to other storage media (10,000 to 100,000x).

If you want to erase the CD because the data in it is confidential (security reasons), just burn it in a fireplace or something.

If its just a CD-R (Compact Disc, Recordable) You are out of luck. It's not going to be possible to delete files from it. It will say the type of disc right on the label, on the non-data side of the CD.

If it says CD-RW (Compact Disc, Rewritable), you should be good to go.

If the CD is CDR you can't erase it, it should be CDRW type which you can erase and and write again. As you said that you will be using CDs for artworks, to make sure that the files will not be accessible on CD, just make a scratch on the CD so it will become unreadable.